Docker Cache Warmer

This is a small and simple docker image that runs a cron job to fetch assets from a server that implements caching. It accepts two arguments in the form of environment variables:

• ASSET_PATH_MANIFEST_URL: A place that is readable publicly, and lists one asset per line without the domain.
• HOSTS_COMMAND: A command that returns a list of newline separated hosts. If you want to hard code it you could use something like echo "http://cach1.domain.com\nhttp://cache2.domain.com". For more complex scenarios you could use something like nslookup to find multiple hosts for a dns record, as in the example below.
• CRON_SCHEDULE: This is your basic cron syntax that will state how often to run the command. For example, to run hourly, you'd use this 0 * * * *. Here's a handy calculator if it's helpful. You can also set this to "now" if you just want it to run once and exit.
• DEBUG: If set it will tell you what addresses it's trying to hit in STDOUT

Example

Here's a cache warmer as configured by docker compose:

  cache-warmer:
    image: corylogan/cache-warmer
    environment:
      - ASSET_PATH_MANIFEST_URL="http://mysite/manifest.txt"
      - HOSTS_COMMAND="nslookup docker.com | tail -n +3 | grep ^Address | cut -d ' ' -f 2"
      - CRON_SCHEDULE="0 * * * *"

Notes

I've decided to not use ssl as in my case, and in the case of others, you're operating on a private network that's using public certs.

Feel free to make a pull request if you see a place to make an improvement.