Gitlab-ci configure docker runner for deployment with SSH keys - symfony

Question

I'm trying to use gitlab-ci and capistrano to deploy my symfony application. But I can't deploy using SSH by injecting keys into docker, the script keeps prompting for password when connecting. I'm using a local instance of gitlab.
In gitlab's SSH_PRIVATE_KEY private variable, I added the git user's private key, and in SSH_SERVER_HOSTKEYS, the ssh-keyscan -H 192.168.0.226 command's result.
In file authorized_keys from deploy's .ssh folder, I put the git user's public key.
Here are the configurations files:
gitlab-ci.yml:
image: php:7.1
cache:
paths:
- vendor/
before_script:
# Install dependencies
- bash ci/docker_install.sh > /dev/null
- bash ci/ssh_inject.sh
stages:
- deploy
deploy:
stage: deploy
script:
- apt-get install ruby-full -yqq
- gem install capistrano -v 3.8.0
- gem install capistrano-symfony
- cap production deploy
environment:
name: production
url: http://website.com
only:
- master
ssh_inject.sh: link
#!/bin/bash
set -xe
# Install ssh-agent if not already installed, it is required by Docker.
# (change apt-get to yum if you use a CentOS-based image)
which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )
# Run ssh-agent (inside the build environment)
eval $(ssh-agent -s)
# Add the SSH key stored in SSH_PRIVATE_KEY variable to the agent store
ssh-add <(echo "$SSH_PRIVATE_KEY")
mkdir -p ~/.ssh
[[ -f /.dockerenv ]] && echo "$SSH_SERVER_HOSTKEYS" > ~/.ssh/known_hosts
deploy.rb:
# config valid only for current version of Capistrano
lock '3.8.0'
set :application, 'symfony'
set :repo_url, 'git#gitlab.local:symfony.git'
# Default deploy_to directory is /var/www/my_app_name
set :deploy_to, '/home/symfony'
set :symfony_env, "prod"
set :composer_install_flags, '--no-dev --prefer-dist --no-interaction --optimize-autoloader'
set :symfony_directory_structure, 3
set :sensio_distribution_version, 5
# symfony-standard edition directories
set :app_path, "app"
set :web_path, "web"
set :var_path, "var"
set :bin_path, "bin"
set :app_config_path, "app/config"
set :log_path, "var/logs"
set :cache_path, "var/cache"
set :symfony_console_path, "bin/console"
set :symfony_console_flags, "--no-debug"
# asset management
set :assets_install_path, "web"
set :assets_install_flags, '--symlink'
# Share files/directories between releases
set :linked_files, %w(app/config/parameters.yml)
set :linked_dirs, %w(web/uploads)
# Set correct permissions between releases, this is turned off by default
set :permission_method, false
set :file_permissions_paths, ["var/logs", "var/cache"]
set :file_permissions_users, ["apache"]
before "deploy:updated", "deploy:set_permissions:acl"
after "deploy:updated", "symfony:assetic:dump"
and production.rb:
server '192.168.0.226', user: 'deploy', roles: %w{app db web}
What could be wrong? I tried to set forward_agent to true but it's not working eather.
If I build the docker container manually and install all dependencies, the ssh connexion can be established without asking for password...
Here is the error:
EDIT:
Is there something to add in the runner configuration ? Here it is:
concurrent = 1
check_interval = 0
[[runners]]
name = "Docker runner"
url = "http://gitlab.local/ci"
token = "mytoken"
executor = "docker"
[runners.docker]
tls_verify = false
image = "php:7.1"
privileged = false
disable_cache = false
volumes = ["/cache"]
[runners.cache]

Answer 1

bash ci/ssh_inject.sh does not work because it is run in a different shell. use:
source ./ci/ssh_inject.sh
instead.

Answer 2

You need to create a ssh key on the gitlab runner with the gitlab-runner user.
Then add the pubkey of this key to your server in the authorized_keys file.

Answer 3

Solved by moving ssh_inject.sh content into gitlab-ci.yml.
If anyone has an idea about why it needs to be in gitlab-ci.yml, I'd like to understand.