Monitor multiple Redis servers on Heroku with Datadog

Our main Rails app on Heroku uses multiple redis instances. We have one instance for our job queue, one for caching and one instance for our session store. This is how we setup Datadog to monitor the health of our redis instances.

The setup is based on Datadog's article on monitoring Ruby on Rails on Heroku. So we need to enable the redis integration in Datadog by adding a file at datadog/conf.d/redisdb.yaml with the following content:

init_config:

instances:
  # populated by prerun.sh

Then we need to modify the datadog/prerun.sh script to add the redis instances to the redisdb.yaml file. The script is executed before the Datadog agent is started. The script looks like this:

redis_regex='(\w+)_URL=redis:\/\/([^:]*):([^@]+)@([^:]+):([0-9]*)$'
env | grep "REDIS.*_URL=" | while read -r line ; do
  if [[ $line =~ $redis_regex ]]; then
    {
      echo "  - host: ${BASH_REMATCH[4]}";
      echo "    port: ${BASH_REMATCH[5]}";
      echo "    username: ${BASH_REMATCH[2]}";
      echo "    password: ${BASH_REMATCH[3]}";
      echo "    tags:";
      echo "      - name:${BASH_REMATCH[1]}";
    } >> "$DD_CONF_DIR/conf.d/redisdb.d/conf.yaml"
  fi
done

It will fetch all REDIS_*_URL environment variables and add them to the redisdb.yaml file. The tags section is optional and can be used to add tags to the redis instance. In our case we add a tag with the name of the redis instance.