Automatically updating a working copy on a remote server using Mercurial
Imagine you have two servers: on one server, you have a Mercurial repository with all your code, accessible through http. On the other one, you have a working copy of this code that you are using to test a website. Let’s call the first server REPOS and the second one DEVEL. This article describes how to automatically update the working copy on DEVEL, after an
hg push on REPOS.
In order to do this, the idea is to write a Mercurial hook that will execute after a
hg push on REPOS and will connect through ssh to DEVEL in order to issue the necessary
hg pull and
hg update. It’s fairly easy to do, but it needs some setup on both DEVEL and REPOS in order to work.
Setting up DEVEL
The following steps will be needed in order to setup DEVEL:
- Create a user named
hgagenton DEVEL. The account of this user will be used to connect by ssh from REPOS in order to do the
sudo adduser hgagent
- If REPOS requires a username and password (or an SSH key) in order to do an
hg pull, configure the
authsection of the
hgrcfile of the hgagent user you just created in order to allow it to do an
hg pullwithout needing to provide his username and password interactively
- Do an
hg cloneof the repository you want to update using the hgagent user (this assumes, obviously, that the repository is already accessible on REPOS), so that the files in the clone belong to hgagent, which will therefore be able to do
Setting up REPOS
The following steps are needed in order to set up REPOS:
- If your repository is not publicly accessible, you will need to set it up so that
hgagentcan access it using a username and password or an SSH key
- You will need to generate a pair of SSH keys, in order to allow a non-interactive connection to DEVEL. If your repository uses http or https, I strongly advise you to generate these SSH keys as the user under which your http server runs (most probably
www-data), as when the hook is executed, it will be executed under the
www-datauser (or whatever user your http server runs on). You can use
sudo -u www-data ssh-keygenin order to generate the keys. Note that you shouldn’t create a passphrase for your SSH key.
- Once the keys are generated, you need to copy the public key to the
/home/hgagent/.ssh/authorized_keys. You can use the following command in order to do so:
ssh-copy-id -i /var/www/.ssh/id_dsa.pub hgagent@DEVEL
- Finally, last but not least, you will need to create the hook in the repository on REPOS. In the .hg/hgrc file of the repository, add the following lines:
[hook] changegroup = ssh hgagent@DEVEL "cd /path/to/working/copy; hg pull; hg update"
That’s it ! When you issue a
hg push on REPOS, it should now automatically connect by ssh to the DEVEL server and update your working copy.