Integration tests: Parse agent version from version.go

[pazone]

What does this PR do?

The way how we defined the agent version for integration tests wasn't reliable. It works correctly on the main branch but might work incorrectly on 8.17. That blocks the backports to 8.17 and 8.16. The new approach parses version.go.

• Modified integration test scripts
• The regexes will be replaced and simplified when this issue is done

Why is it important?

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

• Relates https://github.com/elastic/ingest-dev/issues/4585

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[v1v]

I see this in two places, do you mind moving this logic to a make goal or something else? Otherwise, it's hard to maintain.

For instance, the APM Server uses:

• https://github.com/elastic/apm-server/blob/42e0cbf5b049a92b5536f34090b15f5eb0a7167e/go.mk#L11
• and https://github.com/elastic/apm-server/blob/42e0cbf5b049a92b5536f34090b15f5eb0a7167e/Makefile#L146-L149

Therefore the call is as simple as this https://github.com/elastic/apm-server/blob/42e0cbf5b049a92b5536f34090b15f5eb0a7167e/.buildkite/scripts/dra.sh#L39

[pazone]

What is the second place? If it's the PS file for Windows then unfortunately it's hard to avoid(Possible but the solution is controversial).
I also added a comment above(in the code). The mentioned issue will replace it with AGENT_VERSION=$(cat .agent-version).
I would like to ask you a QQ about your example if you don't mind. Wouldn't it be easier to create a similar .version file and embed it to the version.go? Then getting the version will be as simple as it mentioned above

[v1v]

What is the second place? If it's the PS file for Windows then unfortunately it's hard to avoid(Possible but the solution is controversial).

Yep

Wouldn't it be easier to create a similar .version file and embed it to the version.go?

I think so, thanks for bringing this to my attention, if there is a plan, then all good.