Posts Tagged Kubernetes
Architecting Cloud-Optimized Apps with AKS (Azure’s Managed Kubernetes), Azure Service Bus, and Cosmos DB
An earlier post, Eventual Consistency: Decoupling Microservices with Spring AMQP and RabbitMQ, demonstrated the use of a message-based, event-driven, decoupled architectural approach for communications between microservices, using Spring AMQP and RabbitMQ. This distributed computing model is known as eventual consistency. To paraphrase microservices.io, ‘using an event-driven, eventually consistent approach, each service publishes an event whenever it updates its data. Other services subscribe to events. When an event is received, a service (subscriber) updates its data.’
That earlier post illustrated a fairly simple example application, the Voter API, consisting of a set of three Spring Boot microservices backed by MongoDB and RabbitMQ, and fronted by an API Gateway built with HAProxy. All API components were containerized using Docker and designed for use with Docker CE for AWS as the Container-as-a-Service (CaaS) platform.
Optimizing for Kubernetes on Azure
This post will demonstrate how a modern application, such as the Voter API, is optimized for Kubernetes in the Cloud (Kubernetes-as-a-Service), in this case, AKS, Azure’s new public preview of Managed Kubernetes for Azure Container Service. According to Microsoft, the goal of AKS is to simplify the deployment, management, and operations of Kubernetes. I wrote about AKS in detail, in my last post, First Impressions of AKS, Azure’s New Managed Kubernetes Container Service.
In addition to migrating to AKS, the Voter API will take advantage of additional enterprise-grade Azure’s resources, including Azure’s Service Bus and Cosmos DB, replacements for the Voter API’s RabbitMQ and MongoDB. There are several architectural options for the Voter API’s messaging and NoSQL data source requirements when moving to Azure.
- Keep Dockerized RabbitMQ and MongoDB – Easy to deploy to Kubernetes, but not easily scalable, highly-available, or manageable. Would require storage optimized Azure VMs for nodes, node affinity, and persistent storage for data.
- Replace with Cloud-based Non-Azure Equivalents – Use SaaS-based equivalents, such as CloudAMQP (RabbitMQ-as-a-Service) and MongoDB Atlas, which will provide scalability, high-availability, and manageability.
- Replace with Azure Service Bus and Cosmos DB – Provides all the advantages of SaaS-based equivalents, and additionally as Azure resources, benefits from being in the Azure Cloud alongside AKS.
The Kubernetes resource files and deployment scripts used in this post are all available on GitHub. This is the only project you need to clone to reproduce the AKS example in this post.
git clone \ --branch master --single-branch --depth 1 --no-tags \ https://github.com/garystafford/azure-aks-sb-cosmosdb-demo.git
The Docker images for the three Spring microservices deployed to AKS, Voter, Candidate, and Election, are available on Docker Hub. Optionally, the source code, including Dockerfiles, for the Voter, Candidate, and Election microservices, as well as the Voter Client are available on GitHub, in the
git clone \ --branch kub-aks --single-branch --depth 1 --no-tags \ https://github.com/garystafford/candidate-service.git git clone \ --branch kub-aks --single-branch --depth 1 --no-tags \ https://github.com/garystafford/election-service.git git clone \ --branch kub-aks --single-branch --depth 1 --no-tags \ https://github.com/garystafford/voter-service.git git clone \ --branch kub-aks --single-branch --depth 1 --no-tags \ https://github.com/garystafford/voter-client.git
Azure Service Bus
To demonstrate the capabilities of Azure’s Service Bus, the Voter API’s Spring microservice’s source code has been re-written to work with Azure Service Bus instead of RabbitMQ. A future post will explore the microservice’s messaging code. It is more likely that a large application, written specifically for a technology that is easily portable such as RabbitMQ or MongoDB, would likely remain on that technology, even if the application was lifted and shifted to the Cloud or moved between Cloud Service Providers (CSPs). Something important to keep in mind when choosing modern technologies – portability.
Service Bus is Azure’s reliable cloud Messaging-as-a-Service (MaaS). Service Bus is an original Azure resource offering, available for several years. The core components of the Service Bus messaging infrastructure are queues, topics, and subscriptions. According to Microsoft, ‘the primary difference is that topics support publish/subscribe capabilities that can be used for sophisticated content-based routing and delivery logic, including sending to multiple recipients.’
Since the three Voter API’s microservices are not required to produce messages for more than one other service consumer, Service Bus queues are sufficient, as opposed to a pub/sub model using Service Bus topics.
Cosmos DB, Microsoft’s globally distributed, multi-model database, offers throughput, latency, availability, and consistency guarantees with comprehensive service level agreements (SLAs). Ideal for the Voter API, Cosmos DB supports MongoDB’s data models through the MongoDB API, a MongoDB database service built on top of Cosmos DB. The MongoDB API is compatible with existing MongoDB libraries, drivers, tools, and applications. Therefore, there are no code changes required to convert the Voter API from MongoDB to Cosmos DB. I simply had to change the database connection string.
NGINX Ingress Controller
Although the Voter API’s HAProxy-based API Gateway could be deployed to AKS, it is not optimal for Kubernetes. Instead, the Voter API will use an NGINX-based Ingress Controller. NGINX will serve as an API Gateway, as HAProxy did, previously.
According to NGINX, ‘an Ingress is a Kubernetes resource that lets you configure an HTTP load balancer for your Kubernetes services. Such a load balancer usually exposes your services to clients outside of your Kubernetes cluster.’
An Ingress resource requires an Ingress Controller to function. Continuing from NGINX, ‘an Ingress Controller is an application that monitors Ingress resources via the Kubernetes API and updates the configuration of a load balancer in case of any changes. Different load balancers require different Ingress controller implementations. In the case of software load balancers, such as NGINX, an Ingress controller is deployed in a pod along with a load balancer.’
There are currently two NGINX-based Ingress Controllers available, one from Kubernetes and one directly from NGINX. Both being equal, for this post, I chose the Kubernetes version. There are several advantages of using either version of the NGINX Ingress Controller for Kubernetes, including Layer 4 TCP and UDP and Layer 7 HTTP load balancing, reverse proxying, ease of SSL termination, dynamically-configurable path-based rules, and support for multiple hostnames.
Azure Web App
Lastly, the Voter Client application, not really part of the Voter API, but useful for demonstration purposes, will be converted from a containerized application to an Azure Web App. Since it is not part of the Voter API, separating the Client application from AKS makes better architectural sense. Web Apps are a powerful, richly-featured, yet incredibly simple way to host applications and services on Azure. For more information on using Azure Web Apps, read my recent post, Developing Applications for the Cloud with Azure App Services and MongoDB Atlas.
Revised Component Architecture
Below is a simplified component diagram of the new architecture, including Azure Service Bus, Cosmos DB, and the NGINX Ingress Controller. The new architecture looks similar to the previous architecture, but as you will see, it is actually very different.
To understand the role of each API component, let’s look at one of the event-driven, decoupled process flows, the creation of a new election candidate. In the simplified flow diagram below, an API consumer executes an HTTP POST request containing the new candidate object as JSON. The Candidate microservice receives the HTTP request and creates a new document in the Cosmos DB Voter database. A Spring
RepositoryEventHandler within the Candidate microservice responds to the document creation and publishes a Create Candidate event message, containing the new candidate object as JSON, to the Azure Service Bus Candidate Queue.
Independently, the Voter microservice is listening to the Candidate Queue. Whenever a new message is produced by the Candidate microservice, the Voter microservice retrieves the message off the queue. The Voter microservice then transforms the new candidate object contained in the incoming message to its own candidate data model and creates a new document in its own Voter database.
The same process flows exist between the Election and the Candidate microservices. The Candidate microservice maintains current elections in its database, which are retrieved from the Election queue.
It is useful to understand, the Candidate microservice’s candidate domain model is not necessarily identical to the Voter microservice’s candidate domain model. Each microservice may choose to maintain its own representation of a vote, a candidate, and an election. The Voter service transforms the new candidate object in the incoming message based on its own needs. In this case, the Voter microservice is only interested in a subset of the total fields in the Candidate microservice’s model. This is the beauty of decoupling microservices, their domain models, and their datastores.
The versions of the Voter API microservices used for this post only support Election Created events and Candidate Created events. They do not handle Delete or Update events, which would be necessary to be fully functional. For example, if a candidate withdraws from an election, the Voter service would need to be notified so no one places votes for that candidate. This would normally happen through a Candidate Delete or Candidate Update event.
Provisioning Azure Service Bus
First, the Azure Service Bus is provisioned. Provisioning the Service Bus may be accomplished using several different methods, including manually using the Azure Portal or programmatically using Azure Resource Manager (ARM) with PowerShell or Terraform. I chose to provision the Azure Service Bus and the two queues using the Azure Portal for expediency. I chose the Basic Service Bus Tier of service, of which there are three tiers, Basic, Standard, and Premium.
The application requires two queues, the
candidate.queue, and the
Provisioning Cosmos DB
Next, Cosmos DB is provisioned. Like Azure Service Bus, Cosmos DB may be provisioned using several methods, including manually using the Azure Portal, programmatically using Azure Resource Manager (ARM) with PowerShell or Terraform, or using the Azure CLI, which was my choice.
az cosmosdb create \ --name cosmosdb_instance_name_goes_here \ --resource-group resource_group_name_goes_here \ --location "East US=0" \ --kind MongoDB
The post’s Cosmos DB instance exists within the single East US Region, with no failover. In a real Production environment, you would configure Cosmos DB with multi-region failover. I chose MongoDB as the type of Cosmos DB database account to create. The allowed values are GlobalDocumentDB, MongoDB, Parse. All other settings were left to the default values.
The three Spring microservices each have their own database. You do not have to create the databases in advance of consuming the Voter API. The databases and the database collections will be automatically created when new documents are first inserted by the microservices. Below, the three databases and their collections have been created and populated with documents.
The GitHub project repository also contains three shell scripts to generate sample vote, candidate, and election documents. The scripts will delete any previous documents from the database collections and generate new sets of sample documents. To use, you will have to update the scripts with your own Voter API URL.
MongoDB Aggregation Pipeline
Each of the three Spring microservices uses Spring Data MongoDB, which takes advantage of MongoDB’s Aggregation Framework. According to MongoDB, ‘the aggregation framework is modeled on the concept of data processing pipelines. Documents enter a multi-stage pipeline that transforms the documents into an aggregated result.’ Below is an example of aggregation from the Candidate microservice’s
Aggregation aggregation = Aggregation.newAggregation( match(Criteria.where("election").is(election)), group("candidate").count().as("votes"), project("votes").and("candidate").previousOperation(), sort(Sort.Direction.DESC, "votes") );
To use MongoDB’s aggregation framework with Cosmos DB, it is currently necessary to activate the MongoDB Aggregation Pipeline Preview Feature of Cosmos DB. The feature can be activated from the Azure Portal, as shown below.
Cosmos DB Emulator
Be warned, Cosmos DB can be very expensive, even without database traffic or any Production-grade bells and whistles. Be careful when spinning up instances on Azure for learning purposes, the cost adds up quickly! In less than ten days, while writing this post, my cost was almost US$100 for the Voter API’s Cosmos DB instance.
I strongly recommend downloading the free Azure Cosmos DB Emulator to develop and test applications from your local machine. Although certainly not as convenient, it will save you the cost of developing for Cosmos DB directly on Azure.
With Cosmos DB, you pay for reserved throughput provisioned and data stored in containers (a collection of documents or a table or a graph). Yes, that’s right, Azure charges you per MongoDB collection, not even per database. Azure Cosmos DB’s current pricing model seems less than ideal for microservice architectures, each with their own database instance.
By default the reserved throughput, billed as Request Units (RU) per second or RU/s, is set to 1,000 RU/s per collection. For development and testing, you can reduce each collection to a minimum of 400 RU/s. The Voter API creates five collections at 1,000 RU/s or 5,000 RU/s total. Reducing this to a total of 2,000 RU/s makes Cosmos DB marginally more affordable to explore.
Building the AKS Cluster
An existing Azure Resource Group is required for AKS. I chose to use the latest available version of Kubernetes, 1.8.2.
az login \ --username your_username \ --password your_password az group create \ --resource-group resource_group_name_goes_here \ --location eastus az aks create \ --name cluser_name_goes_here \ --resource-group resource_group_name_goes_here \ --ssh-key-value path_to_your_public_key \ --kubernetes-version 1.8.2 kubectl get nodes --output=wide
By default, AKS will provision a three-node Kubernetes cluster using Azure’s Standard D1 v2 Virtual Machines. According to Microsoft, ‘D series VMs are general purpose VM sizes provide balanced CPU-to-memory ratio. They are ideal for testing and development, small to medium databases, and low to medium traffic web servers.’ Azure D1 v2 VM’s are based on Linux OS images, currently Debian 8 (Jessie), with 1 vCPU and 3.5 GB of memory. By default with AKS, each VM receives 30 GiB of Standard HDD attached storage.
You should always select the type and quantity of the cluster’s VMs and their attached storage, optimized for estimated traffic volumes and the specific workloads you are running. This can be done using the
--node-osdisk-size arguments with the
az aks create command.
The Voter API resources are deployed to its own Kubernetes Namespace,
voter-api. The NGINX Ingress Controller resources are deployed to a different namespace,
ingress-nginx. Separate namespaces help organize individual Kubernetes resources and separate different concerns.
voter-api namespace is created. Then, five required Kubernetes Secrets are created within the namespace. These secrets all contain sensitive information, such as passwords, that should not be shared. There is one secret for each of the three Cosmos DB database connection strings, one secret for the Azure Service Bus connection string, and one secret for the Let’s Encrypt SSL/TLS certificate and private key, used for secure HTTPS access to the Voter API.
The Voter API’s secrets are used to populate environment variables within the pod’s containers. The environment variables are then available for use within the containers. Below is a snippet of the Voter pods resource file showing how the Cosmos DB and Service Bus connection strings secrets are used to populate environment variables.
env: - name: AZURE_SERVICE_BUS_CONNECTION_STRING valueFrom: secretKeyRef: name: azure-service-bus key: connection-string - name: SPRING_DATA_MONGODB_URI valueFrom: secretKeyRef: name: azure-cosmosdb-voter key: connection-string
Shown below, the Cosmos DB and Service Bus connection strings secrets have been injected into the Voter container and made available as environment variables to the microservice’s executable JAR file on start-up. As environment variables, the secrets are visible in plain text. Access to containers should be tightly controlled through Kubernetes RBAC and Azure AD, to ensure sensitive information, such as secrets, remain confidential.
Next, the three Kubernetes ReplicaSet resources, corresponding to the three Spring microservices, are created using Deployment controllers. According to Kubernetes, a Deployment that configures a ReplicaSet is now the recommended way to set up replication. The Deployments specify three replicas of each of the three Spring Services, resulting in a total of nine Kubernetes Pods.
Each pod, by default, will be scheduled on a different node if possible. According to Kubernetes, ‘the scheduler will automatically do a reasonable placement (e.g. spread your pods across nodes, not place the pod on a node with insufficient free resources, etc.).’ Note below how each of the three microservice’s three replicas has been scheduled on a different node in the three-node AKS cluster.
Next, the three corresponding Kubernetes ClusterIP-type Services are created. And lastly, the Kubernetes Ingress is created. According to Kubernetes, the Ingress resource is an API object that manages external access to the services in a cluster, typically HTTP. Ingress provides load balancing, SSL termination, and name-based virtual hosting.
The Ingress configuration contains the routing rules used with the NGINX Ingress Controller. Shown below are the routing rules for each of the three microservices within the Voter API. Incoming API requests are routed to the appropriate pod and service port by NGINX.
apiVersion: extensions/v1beta1 kind: Ingress metadata: name: voter-ingress namespace: voter-api annotations: ingress.kubernetes.io/ssl-redirect: "true" spec: tls: - hosts: - api.voter-demo.com secretName: api-voter-demo-secret rules: - http: paths: - path: /candidate backend: serviceName: candidate servicePort: 8080 - path: /election backend: serviceName: election servicePort: 8080 - path: /voter backend: serviceName: voter servicePort: 8080
The screengrab below shows all of the Voter API resources created on AKS.
NGINX Ingress Controller
After completing the deployment of the Voter API, the NGINX Ingress Controller is created. It starts with creating the
ingress-nginx namespace. Next, the NGINX Ingress Controller is created, consisting of the NGINX Ingress Controller, three Kubernetes ConfigMap resources, and a default back-end application. The Controller and backend each have their own Service resources. Like the Voter API, each has three replicas, for a total of six pods. Together, the Ingress resource and NGINX Ingress Controller manage traffic to the Spring microservices.
The screengrab below shows all of the NGINX Ingress Controller resources created on AKS.
The NGINX Ingress Controller Service, shown above, has an external public IP address associated with itself. This is because that Service is of the type, Load Balancer. External requests to the Voter API will be routed through the NGINX Ingress Controller, on this IP address.
kind: Service apiVersion: v1 metadata: name: ingress-nginx namespace: ingress-nginx labels: app: ingress-nginx spec: externalTrafficPolicy: Local type: LoadBalancer selector: app: ingress-nginx ports: - name: http port: 80 targetPort: http - name: https port: 443 targetPort: https
If you are only using HTTPS, not HTTP, then the references to HTTP and port 80 in the Ingress configuration are unnecessary. The NGINX Ingress Controller’s resources are explained in detail in the GitHub documentation, along with further configuration instructions.
To provide convenient access to the Voter API and the Voter Client, my domain,
voter-demo.com, is associated with the public IP address associated with the Voter API Ingress Controller and with the public IP address associated with the Voter Client Azure Web App. DNS configuration is done through Azure’s DNS Zone resource.
TXT type records might not look as familiar as the
A type records. The
TXT records are required to associate the domain entries with the Voter Client Azure Web App. Browsing to http://www.voter-demo.com or simply http://voter-demo.com brings up the Voter Client.
The Client sends and receives data via the Voter API, available securely at https://api.voter-demo.com.
Routing API Requests
With the Pods, Services, Ingress, and NGINX Ingress Controller created and configured, as well as the Azure Layer 4 Load Balancer and DNS Zone, HTTP requests from API consumers are properly and securely routed to the appropriate microservices. In the example below, three back-to-back requests are made to the
voter/info API endpoint. HTTP requests are properly routed to one of the three Voter pod replicas using the default round-robin algorithm, as proven by the observing the different hostnames (pod names) and the IP addresses (private pod IPs) in each HTTP response.
Shown below is the final Voter API Azure architecture. To simplify the diagram, I have deliberately left out the three microservice’s ClusterIP-type Services, the three default back-end application pods, and the default back-end application’s ClusterIP-type Service. All resources shown below are within the single East US Azure region, except DNS, which is a global resource.
Shown below is the new Azure Resource Group created by Azure during the AKS provisioning process. The Resource Group contains the various resources required to support the AKS cluster, NGINX Ingress Controller, and the Voter API. Necessary Azure resources were automatically provisioned when I provisioned AKS and when I created the new Voter API and NGINX resources.
In addition to the Resource Group above, the original Resource Group contains the AKS Container Service resource itself, Service Bus, Cosmos DB, and the DNS Zone resource.
The Voter Client Web App, consisting of the Azure App Service and App Service plan resource, is located in a third, separate Resource Group, not shown here.
Cleaning Up AKS
A nice feature of AKS, running a
az aks delete command will delete all the Azure resources created as part of provisioning AKS, the API, and the Ingress Controller. You will have to delete the Cosmos DB, Service Bus, and DNS Zone resources, separately.
az aks delete \ --name cluser_name_goes_here \ --resource-group resource_group_name_goes_here
Taking advantage of Kubernetes with AKS, and the array of Azure’s enterprise-grade resources, the Voter API was shifted from a simple Docker architecture to a production-ready solution. The Voter API is now easier to manage, horizontally scalable, fault-tolerant, and marginally more secure. It is capable of reliably supporting dozens more microservices, with multiple replicas. The Voter API will handle a high volume of data transactions and event messages.
There is much more that needs to be done to productionalize the Voter API on AKS, including:
- Add multi-region failover of Cosmos DB
- Upgrade to Service Bus Standard or Premium Tier
- Optimized Azure VMs and storage for anticipated traffic volumes and application-specific workloads
- Implement Kubernetes RBAC
- Add Monitoring, logging, and alerting with Envoy or similar
- Secure end-to-end TLS communications with Itsio or similar
- Secure the API with OAuth and Azure AD
- Automate everything with DevOps – AKS provisioning, testing code, creating resources, updating microservices, and managing data
All opinions in this post are my own, and not necessarily the views of my current or past employers or their clients.
Kubernetes as a Service
On October 24, 2017, less than a month prior to writing this post, Microsoft released the public preview of Managed Kubernetes for Azure Container Service (AKS). According to Microsoft, the goal of AKS is to simplify the deployment, management, and operations of Kubernetes. According to Gabe Monroy, PM Lead, Containers @ Microsoft Azure, in a blog post, AKS ‘features an Azure-hosted control plane, automated upgrades, self-healing, easy scaling.’ Monroy goes on to say, ‘with AKS, customers get the benefit of open source Kubernetes without complexity and operational overhead.’
Unquestionably, Kubernetes has become the leading Container-as-a-Service (CaaS) choice, at least for now. Along with the release of AKS by Microsoft, there have been other recent announcements, which reinforce Kubernetes dominance. In late September, Rancher Labs announced the release of Rancher 2.0. According to Rancher, Rancher 2.0 would be based on Kubernetes. In mid-October, at DockerCon Europe 2017, Docker announced they were integrating Kubernetes into the Docker platform. Even AWS seems to be warming up to Kubernetes, despite their own ECS, according to sources. There are rumors AWS will announce a Kubernetes offering at AWS re:Invent 2017, starting a week from now.
Being a big fan of both Azure and Kubernetes, I decided to give AKS a try. I chose to deploy an existing, simple, multi-tier web application, which I had used in several previous posts, including Eventual Consistency: Decoupling Microservices with Spring AMQP and RabbitMQ. All the code used for this post is available on GitHub.
The application, the Voter application, is composed of an AngularJS frontend client-side UI, and two Java Spring Boot microservices, both backed by individual MongoDB databases, and fronted with an HAProxy-based API Gateway. The AngularJS UI calls the API Gateway, which in turn calls the Spring services. The two microservices communicate with each other using HTTP-based inter-process communication (IPC). Although I would prefer event-based service-to-service IPC, HTTP-based IPC was simpler to implement, for this post.
Interestingly, the Voter application was designed using Docker Community Edition for Mac and deployed to AWS using Docker Community Edition for AWS. Not only would this be my chance to preview AKS, but also an opportunity to compare the ease of developing for Docker CE on AWS using a Mac, to developing for Kubernetes with AKS using Docker Community Edition for Windows.
In order to develop for AKS on my Windows 10 Enterprise workstation, I first made sure I had the latest copies of the following software:
- Docker CE for Windows (v17.11.0)
- Azure CLI (v2.0.21)
- kubectl (v1.8.3)
- kompose (v1.4.0)
- Windows PowerShell (v5.1)
If you are following along with the post, make sure you have the latest version of the Azure CLI, minimally 2.0.21, according to the Azure CLI release notes. Also, I happen to be running the latest version of Docker CE from the Edge Channel. However, either channel’s latest release of Docker CE for Windows should work for this post. Using PowerShell is optional. I prefer PowerShell over working from the Windows Command Prompt, if for nothing else than to preserve my command history, by default.
Kubernetes Resources with Kompose
Originally developed for Docker CE, the Voter application stack was defined in a single Docker Compose file.
To work on AKS, the application stack’s configuration needs to be reproduced as Kubernetes configuration files. Instead of writing the configuration files manually, I chose to use kompose. Kompose is described on its website as ‘a conversion tool for Docker Compose to container orchestrators such as Kubernetes.’ Using kompose, I was able to automatically convert the Docker Compose file into analogous Kubernetes resource configuration files.
kompose convert -f docker-compose.yml
For the AngularJS Client Service and the HAProxy API Gateway Service, I had to modify the Service configuration files to switch the Service type to a Load Balancer (
type: LoadBalancer). Being a Load Balancer, Kubernetes will assign a publically accessible IP address to each Service; the reasons for which are explained later in the post.
The MongoDB service requires a persistent storage volume. To accomplish this with Kubernetes, kompose created a PersistentVolumeClaims resource configuration file. I did have to create a corresponding PersistentVolume resource configuration file. It was also necessary to modify the PersistentVolumeClaims resource configuration file, specifying the Storage Class Name as manual, to correspond to the AKS Storage Class configuration (
From the original Docker Compose file, containing five Docker services, I ended up with a dozen individual Kubernetes resource configuration files. Individual configuration files are optimal for fine-grain management of Kubernetes resources. The Docker Compose file and the Kubernetes resource configuration files are included in the GitHub project.
git clone \ --branch master --single-branch --depth 1 --no-tags \ https://github.com/garystafford/azure-aks-demo.git
Creating AKS Resources
New AKS Feature Flag
According to Microsoft, to start with AKS, while still a preview, creating new clusters requires a feature flag on your subscription.
az provider register -n Microsoft.ContainerService
Using a brand new Azure account for this demo, I also needed to activate two additional feature flags.
az provider register -n Microsoft.Network az provider register -n Microsoft.Compute
If you are missing required features flags, you will see errors, similar to. the below error.
Operation failed with status: ’Bad Request’. Details: Required resource provider registrations Microsoft.Compute,Microsoft.Network are missing.
AKS requires an Azure Resource Group for AKS. I chose to create a new Resource Group, using the Azure CLI.
az group create \ --resource-group resource_group_name_goes_here \ --location eastus
New Kubernetes Cluster
aks feature of the Azure CLI version 2.0.21 or later, I provisioned a new Kubernetes cluster. By default, Azure will create a 3-node cluster. You can override the default number of nodes using the
--node-count parameter; I chose one node. The version of Kubernetes you choose is also configurable using the
--kubernetes-version parameter. I selected the latest Kubernetes version available with AKS, 1.8.2.
az aks create \ --name cluser_name_goes_here \ --resource-group resource_group_name_goes_here \ --node-count 1 \ --generate-ssh-keys \ --kubernetes-version 1.8.2
The newly created Azure Resource Group and AKS Kubernetes Cluster were both then visible on the Azure Portal.
In addition to the new Resource Group I created, Azure also created a second Resource Group containing seven Azure resources. These Azure resources include a Virtual Machine (the single Kubernetes node), Network Security Group, Network Interface, Virtual Network, Route Table, Disk, and an Availability Group.
With AKS up and running, I used another Azure CLI command to create a proxy connection to the Kubernetes Dashboard, which was deployed automatically and was running within the new AKS Cluster. The Kubernetes Dashboard is a general purpose, web-based UI for Kubernetes clusters.
az aks browse \ --name cluser_name_goes_here \ --resource-group resource_group_name_goes_here
Although no applications were deployed to AKS, yet, there were several Kubernetes components running within the AKS Cluster. Kubernetes components running within the kube-system Namespace, included heapster, kube-dns, kubernetes-dashboard, kube-proxy, kube-svc-redirect, and tunnelfront.
Deploying the Application
MongoDB should be deployed first. Both the Voter and Candidate microservices depend on MongoDB. MongoDB is composed of four Kubernetes resources, a Deployment resource, Service resource, PersistentVolumeClaim resource, and PersistentVolume resource. I used
kubectl, the command line interface for running commands against Kubernetes clusters, to create the four MongoDB resources, from the configuration files.
kubectl create \ -f voter-data-vol-persistentvolume.yaml \ -f voter-data-vol-persistentvolumeclaim.yaml \ -f mongodb-deployment.yaml \ -f mongodb-service.yaml
After MongoDB was deployed and running, I created the four remaining Deployment resources, Client, Gateway, Voter, and Candidate, from the Deployment resource configuration files. According to Kubernetes, ‘a Deployment controller provides declarative updates for Pods and ReplicaSets. You describe a desired state in a Deployment object, and the Deployment controller changes the actual state to the desired state at a controlled rate.’
Lastly, I created the remaining Service resources from the Service resource configuration files. According to Kubernetes, ‘a Service is an abstraction which defines a logical set of Pods and a policy by which to access them.’
Switching back to the Kubernetes Dashboard, the Voter application components were now visible.
There were five Kubernetes Pods, one for each application component. Since there is only one Node in the Kubernetes Cluster, all five Pods were deployed to the same Node. There were also five corresponding Kubernetes Deployments.
Similarly, there were five corresponding Kubernetes ReplicaSets, the next-generation Replication Controller. There were also five corresponding Kubernetes Services. Note the Gateway and Client Services have an External Endpoint (External IP) associated with them. The IPs were created as a result of adding the Load Balancer Service type to their Service resource configuration files, mentioned earlier.
Lastly, note the Persistent Disk Claim for MongoDB, which had been successfully bound.
Switching back to the Azure Portal, following the application deployment, there were now three additional resources in the AKS Resource Group, a new Azure Load Balancer and two new Public IP Addresses. The Load Balancer is used to balance the Client and Gateway Services, which both have public IP addresses.
To confirm the Gateway, Voter, and Candidate Services were reachable, using the public IP address of the Gateway Service, I browsed to HAProxy’s Statistics web page. Note the two backends, candidate and voter. The green color means HAProxy was able to successfully connect to both of these Services.
Accessing the Application
The Voter application’s AngularJS UI frontend can be accessed using the Client Service’s public IP address. However, this would not be very user-friendly. Even if I brought up the UI, using the public IP, the UI would be unable to connect to the HAProxy API Gateway, and subsequently, the Voter or Candidate Services. Based on the Client’s current configuration, the Client is expecting to find the Gateway at
To make accessing the Client more user-friendly, and to ensure the Client has access to the Gateway, I provisioned an Azure DNS Zone resource for my domain,
voter-demo.com. I assigned the DNS Zone to the AKS Resource Group.
Within the new DNS Zone, I created three DNS records. The first record, an Alias (A) record, associated
voter-demo.com with the public IP address of the Client Service. I added a second Alias (A) record for the
www subdomain, also associating it with the public IP address of the Client Service. The third Alias (A) record associated the
api subdomain with the public IP address of the Gateway Service.
At a high level, the voter application’s routing architecture looks as follows. The client’s requests to the primary domain or to the
api subdomain are resolved to one of the two public IP addresses configured in the load balancer’s frontend. The requests are passed to the load balancer’s backend pool, containing the single Azure VM, which is the single Kubernetes node, and onto the client or gateway Kubernetes Service. From there, requests are routed to one the appropriate Kubernetes Pods, containing the containerized application components, client or gateway.
Using Chrome’s Developer Tools, observe when a new vote is placed, an HTTP
POST is made to the gateway, on the
http://api.voter-demo.com:8080/voter/votes. The Gateway then proxies this request to the Voter Service, at
http://voter:8080/voter/votes. Since the Gateway and Voter Services both run within the same Cluster, the Gateway is able to use the Voter service’s name to address it, using Kubernetes kube-dns.
In the past, I have developed, deployed, and managed containerized applications, using Rancher, AWS, AWS ECS, native Kubernetes, RedHat OpenShift, Docker Enterprise Edition, and Docker Community Edition. Based on my experience, and given my limited testing with Azure’s public preview of AKS, I am very impressed. Creating the Kubernetes Cluster could not have been easier. Scaling the Cluster, adding Persistent Volumes, and upgrading Kubernetes, is equally as easy. Conveniently, AKS integrates with other Kubernetes tools, like kubectl, kompose, and Helm.
I did run into some minor issues with the AKS Preview, such as being unable to connect to an earlier Cluster, after upgrading from the default Kubernetes version to 1.82. I also experience frequent disconnects when proxying to the Kubernetes Dashboard. I am sure the AKS Preview bugs will be worked out by the time AKS is officially released.
In addition to the many advantages of Kubernetes as a CaaS, a huge advantage of using AKS is the ability to easily integrate Azure’s many enterprise-grade compute, networking, database, caching, storage, and messaging resources. It would require minimal effort to swap out the Voter application’s single containerized version of MongoDB with a highly performant and available instance of Azure Cosmos DB. Similarly, it would be relatively easy to swap out the single containerized version of HAProxy with a fully-featured and secure instance of Azure API Management. The current version of the Voter application replies on RabbitMQ for service-to-service IPC versus this earlier application version’s reliance on HTTP-based IPC. It would be fairly simple to swap RabbitMQ for Azure Service Bus.
Lastly, AKS easily integrates with leading Development and DevOps tooling and processes. Building, managing, and deploying applications to AKS, is possible with Visual Studio, VSTS, Jenkins, Terraform, and Chef, according to Microsoft.
A few good references to get started with AKS:
- Container Orchestration Simplified with Managed Kubernetes in Azure Container Service (AKS)
- Deploy an Azure Container Service (AKS) cluster
- Prepare application for Azure Container Service (AKS)
- Kubernetes Basics
- kubectl Cheat Sheet
All opinions in this post are my own, and not necessarily the views of my current or past employers or their clients.