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Image pull takes a long time to complete in Azure Container Instances

Summary

This article discusses possible causes and solutions for an image pull that takes a long time to complete on Azure Container Instances (ACI).

Prerequisites

Have Azure CLI installed.

Symptoms

The following symptoms can indicate that an image pull is taking a long time to complete:

  • Container groups are stuck in a Creating status for a significant amount of time.
  • The image size is large.

Cause

In ACI, images aren't cached forever. If the image isn't cached, the service pulls the image from the registry. A registry pull can take a long time if the image is large. This behavior is expected for large, uncached images.

If you need faster pull times, check whether one of the listed cached images can work successfully for your use case.

Solution

To view the timeline of the container events, run the following az container show command.

az container show --resource-group <resource-group-name> --name <container-group-name>

The time span between the Pulling and Pulled events helps you determine whether the image pull time is expected or abnormal. The following example shows command output.

{
  "containers": [
    {
      "command": null,
      "environmentVariables": [],
      "image": "pbdockerregistry-on.azurecr.io/<image-name>:<tag>",
      "instanceView": {
        "currentState": {
          "detailStatus": "",
          "exitCode": null,
          "finishTime": null,
          "startTime": "2019-01-22T16:49:11+00:00",
          "state": "Running"
        },
        "events": [
          {
            "count": 1,
            "firstTimestamp": "2019-01-22T16:30:51+00:00",
            "lastTimestamp": "2019-01-22T16:30:51+00:00",
            "message": "pulling image \"pbdockerregistry-on.azurecr.io/<image-name>:<tag>\"",
            "name": "Pulling",
            "type": "Normal"
          },
          {
            "count": 1,
            "firstTimestamp": "2019-01-22T16:48:43+00:00",
            "lastTimestamp": "2019-01-22T16:48:43+00:00",
            "message": "Successfully pulled image \"pbdockerregistry-on.azurecr.io/<image-name>:<tag>\"",
            "name": "Pulled",
            "type": "Normal"
          },
          {
            "count": 1,
            "firstTimestamp": "2019-01-22T16:48:43+00:00",
            "lastTimestamp": "2019-01-22T16:48:43+00:00",
            "message": "Created container with docker id <id>",
            "name": "Created",
            "type": "Normal"
          },
          {
            "count": 1,
            "firstTimestamp": "2019-01-22T16:49:11+00:00",
            "lastTimestamp": "2019-01-22T16:49:11+00:00",
            "message": "Started container with docker id <id>",
            "name": "Started",
            "type": "Normal"
          }
        ],
        "previousState": null,
        "restartCount": 0
      },
      "livenessProbe": null,
      "name": "<container-name>",
      "ports": [
        {
          "port": 443,
          "protocol": "TCP"
        }
      ],
      "readinessProbe": null,
      "resources": {
        "limits": null,
        "requests": {
          "cpu": 4.0,
          "memoryInGb": 4.0
        }
      },
      "volumeMounts": null
    }
  ],
  "diagnostics": null,
  "id": "/subscriptions/<subscription-id>/resourceGroups/<resource-group-name>/providers/Microsoft.ContainerInstance/containerGroups/<container-name>",
  "identity": null,
  "imageRegistryCredentials": [
    {
      "password": null,
      "server": "<user-name>.azurecr.io",
      "username": "<user-name>"
    }
  ],
  "instanceView": {
    "events": [],
    "state": "Running"
  },
  "ipAddress": {
    "dnsNameLabel": "<container-name>",
    "fqdn": "<container-name>.<region>.azurecontainer.io",
    "ip": "<IP>",
    "ports": [
      {
        "port": 443,
        "protocol": "TCP"
      }
    ],
    "type": "Public"
  },
  "location": "<region>",
  "name": "<container-name>",
  "networkProfile": null,
  "osType": "Windows",
  "provisioningState": "Succeeded",
  "resourceGroup": "<resource-group-name>",
  "restartPolicy": "Always",
  "tags": {},
  "type": "Microsoft.ContainerInstance/containerGroups",
  "volumes": null
}

References

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