Disable all datadog agent v6 services together

[pdecat]

This ensures that when datadog_enabled is set to no, the datadog-agent unit is disabled and not started by systemd as a dependency of the datadog-agent-process and datadog-agent-trace units.

Without this change, the datadog-agent unit, while disabled, is started on boot:

[pdecat@packer-5b866036-aaa8-542c-bca5-59e161e9413a]~ $ sudo systemctl status datadog-agent
● datadog-agent.service - "Datadog Agent"
   Loaded: loaded (/lib/systemd/system/datadog-agent.service; disabled; vendor preset: enabled)
   Active: active (running) since Wed 2018-08-29 08:58:52 UTC; 2min 31s ago
 Main PID: 646 (agent)
    Tasks: 8 (limit: 4915)
   CGroup: /system.slice/datadog-agent.service
           └─646 /opt/datadog-agent/bin/agent/agent run -p /opt/datadog-agent/run/agent.pid

[pdecat@packer-5b866036-aaa8-542c-bca5-59e161e9413a]~ $ sudo systemctl is-enabled datadog-agent.service
disabled

[pdecat@packer-5b866036-aaa8-542c-bca5-59e161e9413a]~ $ sudo systemctl is-enabled datadog-agent-trace.service
enabled

[pdecat@packer-5b866036-aaa8-542c-bca5-59e161e9413a]~ $ sudo systemctl is-enabled datadog-agent-process.service
enabled

This is tested on debian stretch with ansible 2.6.3 and systemd 232.

[xp-1000]

It seems to be a relevant change, any news about merging this ?

[filiptepper]

@pdecat Do you think you could make services list configurable? ie. I don't need to run datadog-agent-trace on any of my instances.

[pdecat]

Hi @filiptepper, making the services list configurable would be interesting too but out of the scope of this PR as far as I can tell.

Indeed, the current state without this PR is that the datadog-agent-trace.service and datadog-agent-process.service systemd units are enabled in all cases and actually prevent disabling the datadog-agent.service unit.
This PR is meant to fix just that and does not affect documentation.

Anyway, I glanced at doing what you asked and it seems way more far reaching than I thought.
For starters, the current way to disable the trace and process agents is documented in many places:

      apm_enabled: "true" # has to be set as a string

cf. https://github.com/DataDog/ansible-datadog#example-playbooks

DD_APM_ENABLED - overrides [Main] apm_enabled

cf. https://github.com/DataDog/datadog-trace-agent/blob/master/config/README.md#environment-variables

To control the behavior of the Process Agent, use the enabled variable under the datadog_config field. > It has to be set as a string and the possible values are: "true", "false" (for only container collection) or "disabled" (to disable the Process Agent entirely)

datadog_config:
  process_config:
    enabled: "true" # has to be set as a string

cf. https://github.com/DataDog/ansible-datadog#process-agent

# Enable the process agent.
process_agent_enabled = true

cf. https://github.com/DataDog/datadog-process-agent/tree/master/config#classic-configuration-values-and-how-the-trace-agent-treats-them

DD_PROCESS_AGENT_ENABLED - overrides [Main] process_agent_enabled

cf. https://github.com/DataDog/datadog-process-agent/tree/master/config#environment-variables

In my opinion, that should be addressed in another issue/PR.

[filiptepper]

@pdecat Thanks, that helped a lot!

[pdecat]

Hi @hush-hush, could you please take a look at this one?

[pdecat]

Rebased following the renaming of tasks/agent6.yml to tasks/agent6-linux.yml.

[hush-hush]

Hi @pdecat,

Thanks you for this PR and sorry for the long time it took us to review it.

I added a comment let me know what you think,

[pdecat]

Thanks @hush-hush!

I've renamed the PR to reflect that this only changes the disabling of services.