Entries tagged deployr

Related tags: golang, releases.

Improving my release process

Tuesday, 4 September 2018

I have written a lot of software which I deploy upon my own systems. Typically I deploy these things via puppet, but some things are more ad-hoc. For the ad-hoc deployments I tend to rely upon ssh to deploy them.

I have a bunch of shell-scripts, each called .deploy, which carries out the necessary steps. Here is an example script which deploys my puppet-summary service upon a host:

  #!/bin/sh

  HOST=master.steve.org.uk
  RELEASE=1.2

   # download
  ssh -t ${HOST} "wget --quiet -O /srv/puppet-summary/puppet-summary-linux-amd64-${RELEASE} https://github.com/skx/puppet-summary/releases/download/release-${RELEASE}/puppet-summary-linux-amd64"

   # symlink
   ssh -t ${HOST} "ln -sf /srv/puppet-summary/puppet-summary-linux-amd64-${RELEASE}  /srv/puppet-summary/puppet-summary"

   # make executable
   ssh -t ${HOST} "chmod 755 /srv/puppet-summary/puppet-summary*"

   # restart
   ssh -t ${HOST} "systemctl restart puppet-summary.service"

As you can see this script is very obvious:

  • Download a binary release from a github-page.
  • Symlinks a fixed name to point to this numbered-release.
  • Ensures the download is executable.
  • Then restarts a service.

This whole process is pretty painless, but it assumes prior-setup. For example it assumes that the systemd unit-file is in-place, and any corresponding users, directories, and configuration-files.

I wanted to replace it with something simple to understand, and that replacement system had to have the ability to do two things:

  • Copy a file from my local system to the remote host.
  • Run a command upon the remote host.

That would let me have a local tree of configuration-files, and allow them to be uploaded, and then carry out similar steps to the example above.

Obviously the simplest way to go would be to use fabric, ansible, salt, or even puppet. That would be too easy.

So I wondered could I write a script like this:

   # Copy the service-file into place
   CopyFile puppet-summary.service /lib/systemd/system/puppet-summary.service
   IfChanged "systemctl daemon-reload"
   IfChanged "systemctl enable puppet-summary.service"

   # Fetch the binary
   Run "wget --quiet -O /srv/puppet-summary/puppet-summary-linux-amd64-${RELEASE} https://github.com/skx/puppet-summary/releases/download/release-${RELEASE}/puppet-summary-linux-amd64"

   # Run the rest here ..
   Run "ln -sf .."

   ..
   Run "systemctl restart puppet-summary.service"

Turns out that connecting to a remote-host, via SSH, and using that single connection to either upload/download files or run commands is very simple in golang. So I'm quite placed with that.

I've only added three primitives, and the ability to set/expand variables:

  • CopyFile [local-file-name] [remote-file-name]
    • This sets a flag if the remote file was missing, or the contents changed.
  • IfChanged
    • Run a command only if the file-copy flag was set.
  • Run
    • Run a command. Unconditionally.

I suspect if I needed much more than that I should use something else. But having dealt with Ansible deployments in the past I'm very glad I didn't use that.

(It makes a lot of sense to have the repositories for deploying application A inside the repository of project A. Another reason to not use ansible, etc. Though I guess fabric would work well with that, as recipes are typically contained in ./fabfile.py. Of course .. python.)

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