ArgoCD “ssh: handshake failed... connection reset by peer” when connecting to GitLab via SSH

I’m trying to connect ArgoCD to a private GitLab repository using SSH.

I created a key pair and added the public key to GitLab. Then I configured the private key and repository URL (git@gitlab.example.com:group/repo.git) in ArgoCD.

When I test the connection, I get this error:

Unable to connect SSH repository: error testing repository connectivity:
unable to ls-remote HEAD on repository:
failed to list refs: ssh: handshake failed:
read tcp <argo-ip>:<port>-><gitlab-ip>:22: read: connection reset by peer

What I’ve tried so far:

Added 'insecure: true' to argocd-cm under repositories
Set GIT_SSH_COMMAND="ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null" in the argocd-repo-server Deployment environment variables
Used different key types (RSA, OpenSSH, ED25519)

Still getting the same "handshake failed" error.

If I kubectl exec into another pod in the same cluster and run:

export GIT_SSH_COMMAND="ssh -i ~/.ssh/id_rsa -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null"
git clone git@gitlab.example.com:group/repo.git

…it works perfectly. So network connectivity to GitLab is fine from other pods — the issue seems to be specific to ArgoCD or its SSH client configuration.

Solution

If I remember right, Argo CD uses the go-git SSH client and ignores GIT_SSH_COMMAND (and similar flags). I’m not sure how you added the key, but the recommended way is a repository Secret per the docs

apiVersion: v1
kind: Secret
metadata:
  name: private-repo
  namespace: argocd
  labels:
    argocd.argoproj.io/secret-type: repository
stringData:
  type: git
  url: ssh://git@github.com/argoproj/my-private-repository.git
  sshPrivateKey: |
    -----BEGIN OPENSSH PRIVATE KEY-----
    ...
    -----END OPENSSH PRIVATE KEY-----

also populate argocd-ssh-known-hosts-cm with ssh-keyscan for your Git host.