tedge_mapper az/collectd services start running when the thin-edge device restarts

[PradeepKiruvale]

Proposed changes

Disable the tedge-mapper az/c8y/collectd on installation
Also, start the mappers only if bridge config file exists

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

#1631

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[reubenmiller]

It is better to use the Requires field to list the hard dependency to the collectd.service instead of using the ExecStartPre.

Checkout the systemd docs for more info

[reubenmiller]

Don't we want to enable the starting of the service by default now? As the other services should be prevented from starting due to the ConditionPathExists which will block it from starting if the related mapper files don't exist.

[PradeepKiruvale]

Yup, Removed these.

[reubenmiller]

Few minor changes required

[rina23q]

Looks good, commit messages should be cleaned up before merging though.
Also, better to test the new artifacts before merging especially to check if it doesn't break self-update of tedge_mapper. @gligorisaev has the test case for that already.

[reubenmiller]

Just updating the expected test conditions:

The systemctl service status tedge-mapper-az and tedge-mapper-collectd will retain the the same service state (e.g. either enabled or disabled) as it was prior to the upgrade of thin-edge.io.

For example:

• If the tedge-mapper-az is already enabled prior to the update, then it will continue being enabled
• If the tedge-mapper-az is already disabled prior to the update, then it will continue being disabled

[reubenmiller]

Approved. I verified the test case with @gligorisaev and we have the 👍