Allow users to run custom scripts before starting dd-agent

[apeschel]

This script fixes some white-space issues and adds the ability to run custom scripts before the entrypoint starts dd-agent.

Uses https://github.com/docker-library/mysql as a reference.

[remh]

Thanks @apeschel
Can you explain your use case a bit more please ?

[apeschel]

@remh I would like to be able to put a config template into the /etc/dd-agent/conf.d/mysql.yaml and fill in the password data via an environment variable.

Something like this:

#!/bin/bash

echo "Setting Datadog MySQL password."

sed -i -e "s/XXX_DATADOG_MYSQL_PASSWORD/${DATADOG_MYSQL_PASSWORD}/" /etc/dd-agent/conf.d/mysql.yaml

[christ66]

This might be useful for users who need to decrypt things like usernames/passwords/certificates before the dd-agent runs.

[aerostitch]

Will this be necessary with agent6? Won't it support env variables on the config or would it be only for the core agent?
Also note that the entrypoint executes exec $@ so you should be able to provide a file that you mount from a volume for example and the content of the file would be:

sed -i -e "s/XXX_DATADOG_MYSQL_PASSWORD/${DATADOG_MYSQL_PASSWORD}/" /etc/dd-agent/conf.d/mysql.yaml
supervisord -n -c /etc/dd-agent/supervisor.conf

But I think it would be a big miss if we can't have the support of env variables directly in the integration config (so directly as a PR in dd-agent instead of just here) IMHO.