How to get immediate output from a job run within gitlab-runner? - gitlab

Question

The command gitlab-runner lets you "test" a gitlab job locally. However, the local run of a job seems to have the same problem as a gitlab job run in gitlab CI: The output is not immediate!
What I mean: Even if your code/test/whatever produces printed output, it is not shown immediately in your log or console.
Here is how you can reproduce this behavior (on Linux):
Create a new git repository
mkdir testrepo
cd testrepo
git init
Create file .gitlab-ci.yml with the following content
job_test:
image: python:3.8-buster
script:
- python tester.py
Create a file tester.py with the following content:
import time
for index in range(10):
print(f"{time.time()} test output")
time.sleep(1)
Run this code locally
python tester.py
which produces the output
1648130393.143866 test output
1648130394.1441162 test output
1648130395.14529 test output
1648130396.1466148 test output
1648130397.147796 test output
1648130398.148115 test output
1648130399.148294 test output
1648130400.1494567 test output
1648130401.1506176 test output
1648130402.1508648 test output
with each line appearing on the console every second.
You commit the changes
git add tester.py
git add .gitlab-ci.yml
git commit -m "just a test"
You start the job within a gitlab runner
gitlab-runner exec docker job_test
....
1648130501.9057398 test output
1648130502.9068272 test output
1648130503.9079702 test output
1648130504.9090931 test output
1648130505.910158 test output
1648130506.9112566 test output
1648130507.9120533 test output
1648130508.9131665 test output
1648130509.9142723 test output
1648130510.9154003 test output
Job succeeded
Here you get essentially the same output, but you have to wait for 10 seconds and then you get the complete output at once!
What I want is to see the output as it happens. So like one line every second.
How can I do that for both, the local gitlab-runner and the gitlab CI?

Answer 1

In the source code, this is controlled mostly by the clientJobTrace's updateInterval and forceSendInterval properties.
These properties are not user-configurable. In order to change this functionality, you would have to patch the source code for the GitLab Runner and compile it yourself.
The parameters for the job trace are passed from the newJobTrace function and their defaults (where you would need to alter the source) are defined here.
Also note that the UI for GitLab may not necessarily get the trace in realtime, either. So, even if the runner has sent the trace to GitLab, the javascript responsible for updating the UI only polls for trace data every ~4 or 5 seconds.

Answer 2

You can poll gitlab web for new log lines as fast as you can:
For running job, use url like: https://gitlab.example.sk/grpup/project/-/jobs/42006/trace It will send you a json structure with lines of log file, offset, size and so on. You can have a look at documentation here: https://docs.gitlab.com/ee/api/jobs.html#get-a-log-file
Sidenote: you can use undocumented “state” parameter from response in subsequent request to get only new lines (if any). This is handy.
Through, this does not affect latency of arrival newlines from actual job from runner to gitlab web/backend. See sytech answer for this question.
This answer should help, when there is configured redis cache, incremental logging architecture, and someone wants to get logs from currently running job in "realtime". Polling is still needed through.
Some notes can be found also on forum: https://forum.gitlab.com/t/is-there-an-api-for-getting-live-log-from-running-job/73072