Git(Lab) Pull Mirror

A simple http server that registers and listens to GitHub Push Webhook events to then pull and push back to a GitLab instance.

It's a simple way of having pull mirror (an expensive GitLab-EE feature) for free, with a more responsive implementation.

Usage

git-pull-mirror

This will start the pull mirror webhooks server in the port 9092. It will load the default configuration file mirrors.yml and then will register itself to GitHub using the $CALLBACK_URL such that webhooks will be directed to it.

Environment variables

• CALLBACK_URL callback url to report to github for webhooks, must include schema and domain.
• GITHUB_USER github username, used to configure the webhooks through the API.
• GITHUB_TOKEN github token, used as the password to configure the webhooks through the API
• SSH_KEY is the private ssh key used to talk to the remotes. It needs to be explicitly set, there will be no assumptions made around which ssh key to use.

Options

• -callback.url string callback url to report to github for webhooks, must include schema and domain (default loaded from env CALLBACK_URL)
• -config.file string configuration file (default "mirrors.yml")
• -concurrency int how many background tasks to execute concurrently (default 4)
• -debug enable debugging log level
• -dryrun execute configuration loading then exit. Don't actually do anything
• -git.timeout.seconds int git operations timeout in seconds, defaults to 60 (default 60)
• -github.token string github token, used as the password to configure the webhooks through the API (default loaded from env GITHUB_TOKEN)
• -github.url string api url to register webhooks (default "https://api.github.com/hub")
• -github.user string github username, used to configure the webhooks through the API (default loaded from env GITHUB_USER)
• -listen.address string address in which to listen for webhooks (default ":9092")
• -pprof.address string address in which to listen for pprof debugging requests
• -repositories.path string local path in which to store cloned repositories (default ".")
• -sshkey string ssh key to use to identify to remotes

Signals

git-pull-mirrors supports at least 4 signals:

• SIGINT will perform a graceful shutdown in which it will stop accepting webhooks, then finish all the pending work to then exit.
• SIGHUP will reload the mirrors.yml configuration file and apply it without downtime. If configuration parsing fails, it will not be applied.
• SIGUSR1 will toggle log debugging on and off.
• SIGUSR2 will trigger a full update process for all the registered mirrors

Metrics

git-pull-mirrors offers prometheus metrics used to track the state of the service, these should be used to monitor that the service is operating correctly.

name	type	help
github_webhooks_up	gauge	whether the service is ready to receive requests or not
github_webhooks_repo_up	gauge	whether a repo is succeeding or failing to read or write
github_webhooks_git_latency_seconds	summary	latency percentiles of git fetch and push operations
github_webhooks_hooks_received_total	counter	total count of hooks received
github_webhooks_hooks_retried_total	counter	total number of hooks that failed and were retried
github_webhooks_hooks_updated_total	counter	total number of repos succefully updated
github_webhooks_hooks_failed_total	counter	total number of repos that failed to update for some reason
github_webhooks_boot_time_seconds	gauge	unix timestamp indicating when the process was started
github_webhooks_last_successful_config_apply	gauge	unix timestamp indicating when the last configuration reload was successfully executed

Running

Cloud native way

TODO. C'mon, that's probably one (albeit long) line starting with docker run or kubectl.

Oldschool way

Here are snippets from the instance startup shell script that will install, enable, configure and run the git-pull-mirror as a systemd service in an idempotent way. The exercises of combining them together, managing the secrets, and configuring gitlab.rb so that nginx serves /hooks (hint: no SSL in git-pull-mirror) and /metrics endpoints are left to the reader (hint: nginx['custom_gitlab_server_config'] should do).

Installing:

PULL_MIRROR_VERSION=0.0.6
PULL_MIRROR_BINARY='/usr/local/bin/git-pull-mirror'

if [[ ! -f "$PULL_MIRROR_BINARY" ]]; then
	wget -q -P /tmp "https://github.com/yakshaving-art/git-pull-mirror/releases/download/$PULL_MIRROR_VERSION/git-pull-mirror_${PULL_MIRROR_VERSION}_linux_amd64.tar.gz"
	wget -qO - "https://github.com/yakshaving-art/git-pull-mirror/releases/download/$PULL_MIRROR_VERSION/git-pull-mirror_${PULL_MIRROR_VERSION}_checksums.txt" | \
		sed -n '/linux_amd64/ s|  |  /tmp/|p;' | \
		sha256sum --quiet --check # will crap out on mismatch
	tar zxf "/tmp/git-pull-mirror_${PULL_MIRROR_VERSION}_linux_amd64.tar.gz" -C "$(dirname "$PULL_MIRROR_BINARY")"
	chmod 0755 "$PULL_MIRROR_BINARY"
	rm -f "/tmp/git-pull-mirror_${PULL_MIRROR_VERSION}_linux_amd64.tar.gz"
fi

Adding user and its ssh keys:

PULL_MIRROR_USER="techguru"
PULL_MIRROR_HOME="/home/$PULL_MIRROR_USER"
getent passwd "$PULL_MIRROR_USER" || \
	adduser --home "$PULL_MIRROR_HOME" \
		--disabled-login \
		--disabled-password \
		--gecos "aka The Mirrorbot" \
		"$PULL_MIRROR_USER"

# copy .ssh from secret storage, or regen with:
# ssh-keygen -t ed25519 -C 'MirrorBot key: techguru@mygtlb' -N '' -f id_ed25519_techguru
cp -rp "/path/to/secrets/folder/mirrorbot-.ssh" "$PULL_MIRROR_HOME/.ssh"
chown -R "$PULL_MIRROR_USER:$PULL_MIRROR_USER" "$PULL_MIRROR_HOME"
chmod 0700 "$PULL_MIRROR_HOME/.ssh"
chmod 0400 "$PULL_MIRROR_HOME/.ssh/id_ed25519_techguru"

Set up env file for service (add fingerprints to known_hosts file, or just treat it as secret and copy from secret storage during boot):

test -f /etc/gitlab/git-pull-mirror.conf || cat > /etc/gitlab/git-pull-mirror.conf <<EOF
SSH_KEY=".ssh/id_ed25519_techguru"
SSH_KNOWN_HOSTS=".ssh/known_hosts"
CALLBACK_URL="https://gitlab.my.tld/hooks"
GITHUB_USER="my-cbot"
GITHUB_TOKEN="pszsetme"
EOF

Create systemd unit file (sysV init script left as an exercise for even older school):

cat > /etc/systemd/system/git-pull-mirror.service <<EOF
[Unit]
Description=Git Pull Mirror
After=gitlab-runner.target
ConditionFileIsExecutable=$PULL_MIRROR_BINARY
[Service]
User=$PULL_MIRROR_USER
WorkingDirectory=$PULL_MIRROR_HOME
EnvironmentFile=/etc/gitlab/git-pull-mirror.conf
StartLimitInterval=5
StartLimitBurst=10
ExecStart=$PULL_MIRROR_BINARY -listen.address="127.0.0.1:9092" -config.file="$PULL_MIRROR_HOME/mirrors.yml" -skip.webhooks.registration="true" -debug
Restart=always
RestartSec=120
[Install]
WantedBy=multi-user.target
EOF
chmod 0644 /etc/systemd/system/git-pull-mirror.service

Create mirrors.yml in the proper location:

cat > "$PULL_MIRROR_HOME/mirrors.yml" <<EOF
---
repositories:
- origin: [email protected]:source/source-repo1.git
  target: [email protected]:dst/dst-repo1.git

- origin: [email protected]:source/source-repo2.git
  target: [email protected]:dst/dst-repo2.git
EOF
chown "$PULL_MIRROR_USER:$PULL_MIRROR_USER" "$PULL_MIRROR_HOME/mirrors.yml"
chmod 0644 "$PULL_MIRROR_HOME/mirrors.yml"

Don't forget to add pubkey to both github and gitlab, and do a:

systemctl daemon-reload
systemctl enable git-pull-mirror.service
systemctl start git-pull-mirror.service