If your Checkmk Server is using https, and you're using the Agent Bakery, your SSL Certificate will expire at some time. If the CA for the new certificate stays the same, this should be no problem for the Agent Bakery.


However, if the CA changes, you must follow some extra steps.

Step-by-step guide

  1. Get new certificate

  2. Check if the certificate chain has changed. If:
    • Yes: Jump to step 3
    • No: Jump to step 4

  3. The chain changed
    1. Add the new chain to the Agent Updater (do NOT replace the old chain!). 
    2. Bake and sign agents
    3. Wait until all agents updated
    4. Jump to step 4

  4. The chain did not change, or step 3 was done
    1. restrict Auto Updates to only 2 or 3 hosts, so if something goes wrong, you do not mess up everything
    2. deploy the new certificate to the Apache server
    3. check for the correct cert and chain by using a browser
    4. make sure Auto Update works for the test hosts
    5. if the chain changed (see step 3), remove the old chain from the updater rule, bake & sign agents, and see if everything works with the test hosts
    6. remove the restriction to the test hosts and update all agents.

P.S. to step 3: As this article is written (v2.0.0p8), Checkmk cannot handle the chain correctly if it is contained in a single file. All certs (client, root, intermediate) must be added separately.

If you have everything in one .crt file, this is relatively easy: upload the file & save it, then copy the rule. Checkmk automatically converts the file to text, and now you can split the certificates at their "BEGIN/END Certificate" sections. 

When done, delete the initial rule.