[AIRFLOW-3925] Don't pull docker-images on pretest

[mik-laj]

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Jira

• https://issues.apache.org/jira/browse/AIRFLOW-3925

Description

We do not need a docker in pretest, so we should not pull images.
The problem has previously been discussed:
#4685 (comment)

Tests

No applicable

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

No applicable

Code Quality

No applicable

[codecov-io]

Codecov Report

Merging #4740 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #4740      +/-   ##
=========================================
- Coverage   74.61%   74.6%   -0.01%     
=========================================
  Files         430     430              
  Lines       28002   28002              
=========================================
- Hits        20893   20892       -1     
- Misses       7109    7110       +1

Impacted Files	Coverage Δ
airflow/models/__init__.py	92.59% <0%> (-0.06%)	⬇️

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[codecov-io]

Codecov Report

Merging #4740 into master will decrease coverage by 0.51%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4740      +/-   ##
==========================================
- Coverage   74.61%   74.09%   -0.52%     
==========================================
  Files         430      431       +1     
  Lines       28002    28214     +212     
==========================================
+ Hits        20893    20906      +13     
- Misses       7109     7308     +199

Impacted Files	Coverage Δ
airflow/sensors/sql_sensor.py	57.57% <0%> (-42.43%)	⬇️
airflow/www/api/experimental/endpoints.py	60.74% <0%> (-27.44%)	⬇️
airflow/utils/dag_processing.py	53.12% <0%> (-6.78%)	⬇️
airflow/api/common/experimental/get_code.py	0% <0%> (ø)

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[jmcarp]

This is already included in #4685.

[mik-laj]

I know about it. the purpose of your PR is not to fix the problem presented in this PR, but it does it additionally. Your PR is large and have discussion. I would like this change to come faster, so I made a separate PR.
I added you as a co-author of commit.

[drewsonne]

Also in here #4703 :-)

[jmcarp]

OK, if #4685 and #4703 will take more time to review, let's merge this and start saving time on pre-test steps now.

[ashb]

+1 to the change, but for those of us who aren't familiar with the travis config file (me) could someone explain/point me at docs as to how this stops it pulling a docker image on pre-test?

[drewsonne]

@ashb by default, Travis has the job lifecycles for a single implicit stage ("Test").

When you add the jobs directive, you create new stages, and the jobs in those stages inherit from the default implicit stage ("Test"). So the main part here, is that the jobs define their own actions in the install lifecycle event, which override the inherited install from the default stage ("Test").

I'm not sure if it's made clear on these pages, but this should be the docs for this:

https://docs.travis-ci.com/user/build-stages/#how-do-build-stages-work
https://docs.travis-ci.com/user/job-lifecycle/

[Fokko]

Looks like a great improvements.

Before:

After: