Troubleshoot cluster configurations

Estimated reading time: 2 minutes

Docker UCP persists configuration data on an etcd key-value store that is replicated on all controller nodes of the UCP cluster. This key-value store is for internal use only, and should not be used by other applications.

This article shows how you can access the key-value store, for troubleshooting configuration problems in your cluster.

Using the REST API

In this example we use curl for making requests to the key-value store REST API, and jq to process the responses.

You can install these tools on a Ubuntu distribution by running:

$ sudo apt-get update && apt-get install curl jq

  1. Use a client bundle to authenticate your requests. Learn more.

  2. Use the REST API to access the cluster configurations.

# $DOCKER_HOST and $DOCKER_CERT_PATH are set when using the client bundle
$ export KV_URL="https://$(echo $DOCKER_HOST | cut -f3 -d/ | cut -f1 -d:):12379"

$ curl -s \
    --cert ${DOCKER_CERT_PATH}/cert.pem \
    --key ${DOCKER_CERT_PATH}/key.pem \
    --cacert ${DOCKER_CERT_PATH}/ca.pem \
    ${KV_URL}/v2/keys | jq "."

To learn more about the key-value store rest API check the etcd official documentation.

Using a CLI client

The containers running the key-value store, include etcdctl, a command line client for etcd. You can run it using the docker exec command.

The examples below assume you are logged in with ssh into a UCP controller node.

Check the health of the etcd cluster

$ docker exec -it ucp-kv etcdctl \
        --endpoint https://127.0.0.1:2379 \
        --ca-file /etc/docker/ssl/ca.pem \
        --cert-file /etc/docker/ssl/cert.pem \
        --key-file /etc/docker/ssl/key.pem \
        cluster-health

member 16c9ae1872e8b1f0 is healthy: got healthy result from https://192.168.122.64:12379
member c5a24cfdb4263e72 is healthy: got healthy result from https://192.168.122.196:12379
member ca3c1bb18f1b30bf is healthy: got healthy result from https://192.168.122.223:12379
cluster is healthy

On failure the command exits with an error code, and no output.

To learn more about the etcdctl utility, check the etcd official documentation.

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