Tutorial: Create a highly available Eureka server component cluster in Azure Container Apps

Article
09/13/2024

In this tutorial, you learn to create a Eureka service designed to remain operational in the face of failures and high demand. Building a highly available Eureka service ensures the service registry is always available to clients regardless of demand.

Achieving high availability status for Eureka includes linking multiple Eureka server instances together forming a cluster. The cluster provides resources so that if one Eureka server fails, the other services remain available for requests.

In this tutorial, you:

Create a Eureka server for Spring components.
Bind two Eureka servers for Spring components together into a cluster.
Bind applications to both Eureka servers for highly available service discovery.

Prerequisites

To complete this project, you need the following items:

Requirement	Instructions
Azure account	An active subscription is required. If you don't have one, you can create one for free.
Azure CLI	Install the Azure CLI.

Considerations

When running managed Java components in Azure Container Apps, be aware of the following details:

Item	Explanation
Scope	Components run in the same environment as the connected container app.
Scaling	Component can't scale. The scaling properties `minReplicas` and `maxReplicas` are both set to `1`.
Resources	The container resource allocation for components is fixed. The number of the CPU cores is 0.5, and the memory size is 1Gi.
Pricing	Component billing falls under consumption-based pricing. Resources consumed by managed components are billed at the active/idle rates. You can delete components that are no longer in use to stop billing.
Binding	Container apps connect to a component via a binding. The bindings inject configurations into container app environment variables. Once a binding is established, the container app can read the configuration values from environment variables and connect to the component.

Setup

Use the following steps to create your Eureka service cluster.

Create variables that hold application configuration values.

export LOCATION=chinaeast
export RESOURCE_GROUP=my-services-resource-group
export ENVIRONMENT=my-environment
export EUREKA_COMPONENT_FIRST=eureka01
export EUREKA_COMPONENT_SECOND=eureka02
export APP_NAME=sample-service-eureka-client
export IMAGE="mcr.microsoft.com/javacomponents/samples/sample-service-eureka-client:latest"

az cloud set -n AzureChinaCloud
az login
# az cloud set -n AzureCloud   //means return to Public Azure.

Create a resource group.

az group create --name $RESOURCE_GROUP --location $LOCATION

Create your Container Apps environment.

az containerapp env create \
  --name $ENVIRONMENT \
  --resource-group $RESOURCE_GROUP \
  --location $LOCATION

Create a cluster

Next, create two Eureka server instances and link them together as a cluster.

Create two Eureka Server for Spring components.

az containerapp env java-component eureka-server-for-spring create \
    --environment $ENVIRONMENT \
    --resource-group $RESOURCE_GROUP \
    --name $EUREKA_COMPONENT_FIRST

az containerapp env java-component eureka-server-for-spring create \
    --environment $ENVIRONMENT \
    --resource-group $RESOURCE_GROUP \
    --name $EUREKA_COMPONENT_SECOND

Bind components together

For the Eureka servers to work in a high-availability configuration, they need to be linked together.

Bind the first Eureka server to the second.

az containerapp env java-component eureka-server-for-spring update \
    --environment $ENVIRONMENT \
    --resource-group $RESOURCE_GROUP \
    --name $EUREKA_COMPONENT_FIRST \
    --bind $EUREKA_COMPONENT_SECOND

Bind the second Eureka server to the first.

az containerapp env java-component eureka-server-for-spring update \
    --environment $ENVIRONMENT \
    --resource-group $RESOURCE_GROUP \
    --name $EUREKA_COMPONENT_SECOND \
    --bind $EUREKA_COMPONENT_FIRST

Deploy and bind the application

With the server components linked together, you can create the container app and binding it to the two Eureka components.

Create the container app.

az containerapp create \
    --name $APP_NAME \
    --resource-group $RESOURCE_GROUP \
    --environment $ENVIRONMENT \
    --image $IMAGE \
    --min-replicas 1 \
    --max-replicas 1 \
    --ingress external \
    --target-port 8080

Bind the container app to the first Eureka server component.

az containerapp update \
    --name $APP_NAME \
    --resource-group $RESOURCE_GROUP \
    --bind $EUREKA_COMPONENT_FIRST

Bind the container app to the second Eureka server component.

az containerapp update \
    --name $APP_NAME \
    --resource-group $RESOURCE_GROUP \
    --bind $EUREKA_COMPONENT_SECOND

View the dashboards

Important

To view the dashboard, you need to have at least the Microsoft.App/managedEnvironments/write role assigned to your account on the managed environment resource. You can either explicitly assign Owner or Contributor role on the resource or follow the steps to create a custom role definition and assign it to your account.

Create the custom role definition.

az role definition create --role-definition '{
    "Name": "Java Component Dashboard Access",
    "IsCustom": true,
    "Description": "Can access managed Java Component dashboards in managed environments",
    "Actions": [
        "Microsoft.App/managedEnvironments/write"
    ],
    "AssignableScopes": ["/subscriptions/<SUBSCRIPTION_ID>"]
}'

Make sure to replace placeholder in between the <> brackets in the AssignableScopes value with your subscription ID.

Assign the custom role to your account on managed environment resource.

Get the resource ID of the managed environment.

export ENVIRONMENT_ID=$(az containerapp env show \
  --name $ENVIRONMENT --resource-group $RESOURCE_GROUP \
  --query id -o tsv)

Assign the role to your account.

Before running this command, replace the placeholder in between the <> brackets with your user or service principal ID.
```
az role assignment create \
  --assignee <USER_OR_SERVICE_PRINCIPAL_ID> \
  --role "Java Component Dashboard Access" \
  --scope $ENVIRONMENT_ID
```
Get the URL of the Eureka Server for Spring dashboard.
```
az containerapp env java-component eureka-server-for-spring show \
  --environment $ENVIRONMENT \
  --resource-group $RESOURCE_GROUP \
  --name $EUREKA_COMPONENT_FIRST \
  --query properties.ingress.fqdn -o tsv
```
This command returns the URL you can use to access the Eureka Server for Spring dashboard. Through the dashboard, you can verify that the Eureka server setup consists of two replicas.

Clean up resources

The resources created in this tutorial have an effect on your Azure bill. If you aren't going to use these services long-term, run the following command to remove everything created in this tutorial.

az group delete \
    --resource-group $RESOURCE_GROUP

Next steps

Configure Eureka Server for Spring settings