reorder the COPY in dockerfiles of backend for better layer caching

[Davda-James]

Changes:
Minor improvements were made to the backend dockerfiles by reordering COPY statements. Previously, stable files like settings, static, and templates would rebuild whenever frequently changing files like apps were modified. The COPY instructions have now been reordered so that the most volatile files (apps and tests) are copied last.

Resolves #3944

I have scoped this for backend dockerfiles changes, if suggested by @ahmedxgouda will also review other dockerfiles for such improvements.

Files changed

docker/backend/Dockerfile 
docker/backend/Dockerfile.test

• I followed the contributing workflow
• I verified that my code works as intended and resolves the issue as described
• I ran make check-test locally: all warnings addressed, tests passed
  The mypy test is failing but that is not because of my change its due to unescaped new lines in f string.

backend/tests/apps/mentorship/management/commands/mentorship_sync_module_issues_test.py:210: error: Unterminated string literal (detected at line 210)  [syntax]
Found 1 error in 1 file (errors prevented further checking)

If want I can change that in this PR.

• I used AI for code, documentation, tests, or communication related to this PR

[coderabbitai]

Summary by CodeRabbit

• Chores
  • Reordered Docker build file copy steps to improve layer caching and build efficiency.
  • Adjusted the sequence of asset and application copies to reduce rebuild frequency for unchanged layers and speed up image builds.

Walkthrough

Reorders COPY directives in docker/backend/Dockerfile: moves COPY apps to after COPY templates and COPY static, and adjusts the relative ordering of templates and static. No other build instructions or public APIs were changed.

Changes

Cohort / File(s)	Summary
Dockerfile optimization docker/backend/Dockerfile	Reordered COPY statements: placed COPY templates before COPY static, and moved COPY apps later in the sequence (after templates/static). Added a comment about cache considerations. No other instructions altered.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• Update docker files location #3112 — Similar edits to docker/backend/Dockerfile reordering COPY directives and moving app/entrypoint copies.

Suggested labels

backend, docker

Suggested reviewers

• kasya

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: reordering COPY directives in backend Dockerfiles for improved layer caching.
Description check	✅ Passed	The description clearly explains the rationale for reordering COPY statements to optimize Docker layer caching by placing volatile files last.
Linked Issues check	✅ Passed	The PR successfully addresses issue #3944 by reordering COPY statements in backend Dockerfiles to copy stable files before volatile ones, improving layer caching.
Out of Scope Changes check	✅ Passed	All changes are within scope, focusing on reordering COPY directives in backend Dockerfiles as specified in issue #3944.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

[ahmedxgouda]

Thank you for working on this. Please see the below comments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.34%. Comparing base (6071232) to head (d5f83c5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3945   +/-   ##
=======================================
  Coverage   96.34%   96.34%           
=======================================
  Files         512      512           
  Lines       15815    15815           
  Branches     2131     2174   +43     
=======================================
  Hits        15237    15237           
  Misses        431      431           
  Partials      147      147           

Flag	Coverage Δ
backend	95.99% <ø> (ø)
frontend	97.42% <ø> (ø)

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[cubic-dev-ai]

1 issue found across 2 files (changes from recent commits).

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="docker/backend/Dockerfile.test">

<violation number="1">
P1: **Caching regression**: `COPY apps apps` was moved from the last position to the second, which is the *opposite* of the intended optimization. In Docker layer caching, when a layer changes all subsequent layers are invalidated. The volatile `apps` directory should be copied **last** (not second), so that changes to application code don't invalidate the cache for stable layers like `settings`, `static`, and `templates`.

The correct order should copy stable files first and volatile files (`apps`, `tests/apps`) last — matching the pattern already used in the production `Dockerfile`.</violation>
</file>

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[ahmedxgouda]

LGTM

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud