"docker pull" certificate signed by unknown authority

Question

I was trying to pull a docker image from a docker registry but hit the following issue:

$ docker pull <docker registry>/<image name>/<tag>  Error response from daemon: Get <docker registry>/v1/_ping: x509: certificate signed by unknown authority 

I tried with "curl" and get a similar error message:

 curl performs SSL certificate verification by default, using a "bundle"  of Certificate Authority (CA) public keys (CA certs). If the default  bundle file isn't adequate, you can specify an alternate file  using the --cacert option. 

So I downloaded the CA certificate and imported to the server (RedHat Linux 7) with the following commands:

cp root_cert.cer /etc/pki/ca-trust/source/anchors/ update-ca-trust 

After the root cert is imported, I can see curl is working fine as it won't complain the cert error, however if I use docker pull I still have the same issue. Is docker using different ca-cert location than curl? How do I fix the issue with docker pull in this situation?

Answer 1

• first create a file - /etc/docker/daemon.json

• than run the following to add certs

    openssl s_client -showcerts -connect [registry_address]:[registry_port] < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > /etc/docker/certs.d/[registry_address]/ca.crt 

works without restart

OR

import the cert to system like

• save the cert to the file , like the command above (the port is crucial, no need for the protocol)

   openssl s_client -showcerts -connect [registry_address]:[registry_port] < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ca.crt 

• copy it to /usr/local/share/ca-certificates/

   sudo cp ca.crt /usr/local/share/ca-certificates/ 

• run update-ca-certificates

   sudo update-ca-certificates 

• restart docker !

Answer 2

You may need to restart the docker service to get it to detect the change in OS certificates.

Docker does have an additional location you can use to trust individual registry server CA. You can place the CA cert inside /etc/docker/certs.d/<docker registry>/ca.crt. Include the port number if you specify that in the image tag, e.g in Linux.

/etc/docker/certs.d/my-registry.example.com:5000/ca.crt 

or in Windows 10:

C:\ProgramData\docker\certs.d\ca.crt