SSH Host Key Verification Failed inside GitLab CI

Question

Local Setup

I created a public and private SSH key via the ssh-keygen command.

I decided to setup the private key locally first

Answer 1

You may need to try setting the mode to 644 rather than 700. 644 is what is suggested in the Verifying the SSH host keys documentation, and is also what SSH uses for this file by default. Some parts of SSH are very particular about this - I'm not sure if known_hosts is particular.

The docs also mention you should set the value of SSH_KNOWN_HOSTS variable to the entire output of ssh-keyscan since there are multiple keys.

EDIT:

The following .gitlab-ci.yml worked for me on GitLab.com. Note the use of ~/.ssh/ rather than /.ssh/.

image: ubuntu:latest

test_job:
  script:
  - apt-get update
  - apt-get install openssh-client git-core -y
  - eval $(ssh-agent -s)
  - echo "$SSH_DEPLOY_PRIVATE_KEY" | tr -d '\r' | ssh-add - > /dev/null
  - mkdir -p ~/.ssh && touch ~/.ssh/known_hosts
  - echo "$SSH_KNOWN_HOSTS" >> ~/.ssh/known_hosts
  - git clone git@gitlab.com:gitlab-org/gitlab-ce.git