This is a common docker error when trying to log into their docker registry and the error looks like “x509: certificate signed by unknown authority”.
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Cause of this Issue :
This error happens when you are using a self-signed certificate for your docker registry instead of the certificate issued by the trusted certificate authority (CA). Then the docker daemon will not trust your self-signed certificate and it will lead to the x509 error.
Diagnose the Issue :
You can recreate the issue by trying to log into the docker using the below command ;
docker login <docker_registry_host>:<docker_registry_port> -u user -p password Eg : docker login skynats.com:5666 -u admin -p [email protected]
In case of this certificate issue you will get the below error ;
Error response from daemon : Get https://skynats.com:5666/v2/: x509 certificate signed by unknown authority
To Resolve the Issue :
We can make the docker trust the self-signed certificate by copying the self-signed certificate to the “/etc/docker/certs.d/<docker_registry_hostname>:<docker_registry_host_port>/ca.crt” on the machine where you are trying to run the docker login command.
You can follow the below steps to solve this issue ;
1. Create the following directory on the server from which you are trying to run the docker login command.
mkdir -p /etc/docker/certs.d/<dcoker_registry_host>:<docker_registry_host_port>
2. Copy your Docker registry certificate file from your docker registry host to the cluster where you are running docker login.
You should rename your registry certificate file to “/etc/docker/certs.d/<docker_registry_host>:<docker_registry_host_port>/ca.crt”
scp <your_registry_hostname>:/opt/registry/certs/domain.crt /etc/docker/certs.d/<docker_registry_host>:<docker_registry_host_port>/ca.crt
For example ;
mkdir -p /etc/docker/certs.d/skynats.com:5666 scp skynats.com:/opt/registry/certs/domain.crt /etc/docker/certs.d/skynats.com:5666/ca.crt
3. Then you can try to login into your docker registry again.
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