Even if you are a gerrit/git sysadmin having done a dozen code review setups already, you might get stumped with the ‘reject HostKey’ error when trying to replicate from Gerrit to a Github Enterprise instance.

So this error stems from the following reasons -

  1. Gerrit used Eclipse’s JGit library to implement Git
  2. Github Enterprise enforces ECDSA SSH v2 for SSH connections

Basically this is an issue about JGit not able to parse hashed known_host file lines for ECDSA Protocol 2. But we can neigher change the JCh (as we are using compiled) gerrit, nor can we (or want to) disable ECDSA 2 enforcement in Github Enterprise

So I’ll keep it short and jump to straight to how to solve this.

First we need to set an alias of our Github Enterprise server in ssh config. Edit ~/.ssh/config and add this

Host mygit git.yourserver.com
HostName mygit.yourserver.com
Protocol 2
HostKeyAlgorithms ssh-rsa,ssh-dss

Replace git.yourserver.com with your actual server address. mygit is also upto you. Name it whatever you like

In your $GERRIT_HOME/etc/replication.config in the url fields change references to git@git.yourserver.com to git@mgit

Here is an example from my setup

[remote "internal"]
    url = git@mygit:${name}.git
    projects = yu-aosp-internal/*
    push = +refs/*:refs/*
    timeout = 50
    threads = 4
    replicationDelay = 0
    defaultForceUpdate = true

Purge your ~/.ssh/known_host file. You can just delete the ecdsa lines.

Run ssh -T git@mygit (run it as the same user that runs gerrit - usually it might be user gerrit2 ) to add the ssh remote again.

Now restart gerrit.

Your replications should be working now.