`maxReplicas` in YAML file not respected

[chrisdeely]

Describe the bug

I am using a YAML file to create/update a container app with the az containerapp create command. I have defined a scale configuration as below:

properties:
  template:
    scale:
      minReplicas: 1
      maxReplicas: 1

(While unconventional, my goal is to have exactly 1 replica of this container)

The az containerapp create command validates the YAML file & completes the transaction successfully, however the maxReplicas value is ignored.

In the command output, I can see that internally the YAML was translated to ARM and the scale section incorrectly lists maxReplicas as 10:

"scale": {
        "cooldownPeriod": 300,
        "maxReplicas": 10,
        "minReplicas": 1,
        "pollingInterval": 30,
        "rules": null
      }

Related command

az containerapp create --name ${NAME_LABEL} --resource-group ${AZURE_RESOURCE_GROUP} --yaml ${YAML_FILE}

Errors

No errors, the transaction completes & creates or updates the container app

Issue script & Debug output

Both the outbound request and response body to PUT https://management.azure.com/subscriptions/SUBSCRIPTION/resourceGroups/RESOURCE_GROUP/providers/Microsoft.App/containerApps/APP_NAME show maxReplicas: null

cli.azure.cli.core.util: Request URL: 'https://management.azure.com/subscriptions/SUBSCRIPTION/resourceGroups/RESOURCE_GROUP/providers/Microsoft.App/containerApps/APP_NAME?api-version=2025-01-01'
cli.azure.cli.core.util: Request method: 'PUT'
cli.azure.cli.core.util: Request headers:
cli.azure.cli.core.util:     'User-Agent': 'python/3.13.7 (macOS-15.6.1-arm64-arm-64bit-Mach-O) AZURECLI/2.77.0 (HOMEBREW)'
cli.azure.cli.core.util:     'Accept-Encoding': 'gzip, deflate'
cli.azure.cli.core.util:     'Accept': '*/*'
cli.azure.cli.core.util:     'Connection': 'keep-alive'
cli.azure.cli.core.util:     'x-ms-client-request-id': 'req'
cli.azure.cli.core.util:     'Content-Type': 'application/json'
cli.azure.cli.core.util:     'CommandName': 'containerapp create'
cli.azure.cli.core.util:     'ParameterSetName': '--debug --name --resource-group --yaml'
cli.azure.cli.core.util:     'Authorization': 'Bearer ......'
cli.azure.cli.core.util:     'Content-Length': '3404'
cli.azure.cli.core.util: Request body:
cli.azure.cli.core.util: {"scale": {"minReplicas": 1, "maxReplicas": null, "cooldownPeriod": null, "pollingInterval": null, "rules": null}, 
urllib3.connectionpool: Starting new HTTPS connection (1): management.azure.com:443
urllib3.connectionpool: https://management.azure.com:443 "PUT /subscriptions/SUBSCRIPTION/resourceGroups/RESOURCE_GROUP/providers/Microsoft.App/containerApps/APP_NAME?api-version=2025-01-01 HTTP/1.1" 201 4229
cli.azure.cli.core.util: Response status: 201
cli.azure.cli.core.util: Response headers:
cli.azure.cli.core.util:     'Cache-Control': 'no-cache'
cli.azure.cli.core.util:     'Pragma': 'no-cache'
cli.azure.cli.core.util:     'Content-Length': '4229'
cli.azure.cli.core.util:     'Content-Type': 'application/json; charset=utf-8'
cli.azure.cli.core.util:     'Expires': '-1'
cli.azure.cli.core.util:     'Retry-After': '15'
cli.azure.cli.core.util:     'x-ms-async-operation-timeout': 'PT15M'
cli.azure.cli.core.util:     'api-supported-versions': '2022-03-01, 2022-06-01-preview, 2022-10-01, 2022-11-01-preview, 2023-04-01-preview, 2023-05-01, 2023-05-02-preview, 2023-08-01-preview, 2023-11-02-preview, 2024-02-02-preview, 2024-03-01, 2024-08-02-preview, 2024-10-02-preview, 2025-01-01, 2025-02-02-preview, 2025-07-01, 2025-10-02-preview'
cli.azure.cli.core.util:     'X-Powered-By': 'ASP.NET'
cli.azure.cli.core.util:     'Strict-Transport-Security': 'max-age=31536000; includeSubDomains'
cli.azure.cli.core.util:     'X-Content-Type-Options': 'nosniff'
cli.azure.cli.core.util:     'X-Cache': 'CONFIG_NOCACHE'
cli.azure.cli.core.util:     'Date': 'Thu, 04 Sep 2025 16:16:02 GMT'
cli.azure.cli.core.util: Response content:
cli.azure.cli.core.util: {"id":"/subscriptions/SUBSCRIPTION/resourceGroups/RESOURCE_GROUP/providers/Microsoft.App/containerapps/APP_NAME","name":"APP_NAME","type":"Microsoft.App/containerApps","scale":{"minReplicas":1,"maxReplicas":null,"cooldownPeriod":null,"pollingInterval":null,"rules":null},

Expected behavior

The scale rule's maxReplicas should match what was defined in the YAML config

Environment Summary

az -v
azure-cli 2.77.0

core 2.77.0
telemetry 1.1.0

Dependencies:
msal 1.34.0b1
azure-mgmt-resource 23.3.0

Additional context

If there is an explicit rule against setting maxReplicas: 1 I cannot find any such documentation, and the CLI should throw a validation error.

[yonzhan]

Thank you for opening this issue, we will look into it.

[microsoft-github-policy-service]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @howang-ms, @Greedygre.

[Greedygre]

Hi @chrisdeely

I cannot repro this. I tried with one sample yaml file as following:
az containerapp create -n {} -g {} --environment {} --yaml {} --debug

properties:
  template:
    containers:
    - image: nginx
      name: nginx
      env:
        - name: HTTP_PORT
          value: 80
      command:
        - npm
        - start
      resources:
        cpu: 0.5
        memory: 1Gi
    scale:
      minReplicas: 1
      maxReplicas: 1

And in the requestPayload, the maxReplicas is respected.

cli.azure.cli.core.util: Request URL: 'https://management.azure.com/subscriptions/xxx/resourceGroups/xxx/providers/Microsoft.App/containerApps/xxx?api-version=2025-01-01'
cli.azure.cli.core.util: Request method: 'PUT'
cli.azure.cli.core.util: Request headers:
cli.azure.cli.core.util:     'User-Agent': 'python/3.10.11 (Windows-10-10.0.26100-SP0) AZURECLI/2.77.0 (PIP)'
cli.azure.cli.core.util:     'Accept-Encoding': 'gzip, deflate'
cli.azure.cli.core.util:     'Accept': '*/*'
cli.azure.cli.core.util:     'Connection': 'keep-alive'
cli.azure.cli.core.util:     'x-ms-client-request-id': 'xxx'
cli.azure.cli.core.util:     'Content-Type': 'application/json'
cli.azure.cli.core.util:     'CommandName': 'containerapp create'
cli.azure.cli.core.util:     'ParameterSetName': '-n -g --environment --yaml --debug'
cli.azure.cli.core.util:     'Authorization': 'Bearer ...'
cli.azure.cli.core.util:     'Content-Length': '957'
cli.azure.cli.core.util: Request body:
cli.azure.cli.core.util: {"tags": null, "location": "xxx", "extendedLocation": null, "identity": null, "managedBy": null, "properties": {"environmentId": "xxx", "configuration": null, "template": {"revisionSuffix": null, "terminationGracePeriodSeconds": null, "initContainers": null, "containers": [{"image": "nginx", "name": "nginx", "command": ["npm", "start"], "args": null, "env": [{"name": "HTTP_PORT", "value": "80", "secretRef": nu
ll}], "resources": {"cpu": 0.5, "memory": "1Gi", "ephemeralStorage": null}, "volumeMounts": null, "probes": null}], "scale": {"minReplicas": 1, "maxReplicas": 1, "cooldownPeriod": null, "pollingInterval": null, "rules": null}, "volumes": null, "serviceBinds": null}, "workloadProfileName": null, "latestReadyRevisionName": null, "eventStreamEndpoint": null}}

[Greedygre]

@chrisdeely You can try with the sample YAML file.
Base on your request Body shown, the maxReplicas":null. This means the line for maxReplicas might not be recognized and may not be parsed correctly. Which might relate to the different types of encoding files.

Is the maxReplicas":null at the last line of the file?
Can you try to add an extra blank line at the end and try again?
Also, Can you tell me what is the encoding format of your file?

cli.azure.cli.core.util: {"id":"/subscriptions/SUBSCRIPTION/resourceGroups/RESOURCE_GROUP/providers/Microsoft.App/containerapps/APP_NAME","name":"APP_NAME","type":"Microsoft.App/containerApps","scale":{"minReplicas":1,"maxReplicas":null,"cooldownPeriod":null,"pollingInterval":null,"rules":null},

Thanks

[chrisdeely]

@Greedygre you were exactly correct, there was no newline at the end of the file so the setting was not read! 🤦

Thank you for the speedy response!