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Asked: 2024-09-25T21:10:46+05:30 In: ,

I am encountering an issue when trying to join a Docker Swarm cluster from a Linux container. The error message indicates that the remote certificate authority does not match the expected fingerprint. How can I resolve this problem and successfully connect the container to the swarm?

I’ve been working on setting up a Docker Swarm cluster, and I’m running into a bit of a headache while trying to join a Linux container to the swarm. So here’s the deal: I’ve got everything mostly set up, but every time I attempt to connect the container, I get this error message saying that the remote certificate authority doesn’t match the expected fingerprint.

At first, I thought, “Okay, maybe I missed a step in the setup.” I went back through the documentation and double-checked my swarm initialization processes, but everything seems to be in order. The swarm itself is operational because other nodes can connect just fine. It’s just this one container that’s giving me grief.

What’s puzzling is that I’ve been able to connect other containers without any issues. This particular container has similar configurations to the others, so no clue why it’s acting up. I’ve even tried restarting Docker and cleaning up the network settings, thinking it might help reset something to fix the problem.

I don’t know if this could be related to the way the certificates are being handled, but I’m starting to wonder if there’s an issue with the CA configuration in this container. Has anyone else faced this kind of issue before?

I’ve read that sometimes you need to manually verify the fingerprint or even regenerate the certificates, but I’m not sure where to start with that. If someone could guide me on how to properly check or set the expected fingerprint, or if there are any common troubleshooting steps you think I might be overlooking, I’d really appreciate it!

I just want to get this container into the swarm so I can continue my work without running into these annoying roadblocks. Thanks in advance for any help!

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    2 Answers

    1. “`html

      It sounds like you’ve run into a pretty common issue when it comes to joining a container to a Docker Swarm, especially around certificate mismatches. Here are some things you might want to check:

      • Fingerprint Verification: Make sure you have the correct fingerprint for the swarm’s CA (Certificate Authority). You can check it using the command docker swarm ca --fingerprint on a working node. Then compare that with what your troublesome container is seeing.
      • Regenerate Certificates: If the fingerprints don’t match, it might be worth regenerating the certificates. You can do this using docker swarm ca --rotate. Keep in mind that you’ll need to rejoin your nodes after this since the cluster’s certificates will change.
      • Inspect Network Configurations: Since you’ve tried resetting the network, ensure that there are no firewall rules or any network policies blocking the connection between the nodes and your container.
      • Check Docker Version: Make sure that the version of Docker running on your container is compatible with the Swarm. Running an old version can sometimes lead to unexpected behavior.
      • Logs: Don’t forget to check the Docker logs using docker logs . This can sometimes give you clues about what’s going wrong.

      It might feel a bit overwhelming right now, but just take it step by step. Hopefully, one of these tips can get your container hooked up to the swarm in no time!

      “`

    2. When encountering issues with a container unable to join a Docker Swarm due to a certificate authority mismatch, the first step is to ensure that the Docker daemon running on the problematic container has access to the Docker swarm’s root CA certificate. It’s possible that the container might not have the correct CA certificates, or they may differ from those utilized by the swarm manager. You can verify the expected fingerprint by checking the swarm’s CA certificate using the command docker swarm ca --list on your swarm manager. After confirming the certificate fingerprint, ensure that the container’s environment has access to the CA certificate and is correctly configured to trust it.

      If the environment is already correctly configured and the issue persists, consider regenerating the certificates associated with your swarm. This can be done by running docker swarm init --force-new-cluster on a swarm manager node, which will regenerate all the cryptographic artifacts used in the swarm, but be cautious as this action looks to new swarm management. Before proceeding, ensure that you back up any important data regarding the existing configuration. Additionally, remember to check the service and network configurations as inconsistencies may also lead to connectivity issues. Keeping logs and looking for specific errors can also be helpful in diagnosing the issue.

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