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C2(authentik-source-build): impl update Python backend card with build findings

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Document approach pivot from uv pip download (doesn't exist in uv 0.9.29)
to uv sync FOD + autoPatchelfHook. Record build issue fixes: pg_config,
gssapi S4U headers, xmlsec libltdl, FOD store reference stripping.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Erich Blume 2026-03-01 09:14:30 -08:00
commit f19eb5776f
1 changed files with 30 additions and 13 deletions
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docs/how-to/authentik/authentik-python-backend-derivation.md
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@ -20,26 +20,28 @@ Authentik 2026.2.0 requires Python 3.14 (`requires-python = "==3.14.*"`). The ni
Instead of carrying individual overrides for each broken package, we use **`uv`** to install Python dependencies from PyPI, where upstream maintainers have already published Python 3.14-compatible wheels. Nix provides only the Python interpreter and system libraries.
## Approach: uv + fixed-output derivation
## Approach: uv sync FOD + autoPatchelfHook
Nix builds are sandboxed with no network access. The pattern is:
1. **Fixed-output derivation (FOD)** — downloads all wheels/sdists from PyPI. FODs are allowed network access because the output hash is declared upfront (like `fetchurl`). Locked by authentik's `uv.lock`.
2. **Main derivation** — builds a Python venv from the downloaded packages using `uv pip install --find-links <FOD> --no-index`. No network needed.
1. **Fixed-output derivation (FOD)** — `uv sync --frozen` fetches and installs all dependencies into a venv. FODs are allowed network access because the output hash is declared upfront. Compiled `.so` files reference Nix store paths (RPATHs to libxml2, krb5, etc.), which FODs must not contain, so we strip references with `remove-references-to` and delete `bin/` and `.pyc` files.
2. **Main derivation** — copies the FOD's `lib/python3.14/site-packages/`, recreates `bin/` with proper python symlinks, restores `pyvenv.cfg`, and runs `autoPatchelfHook` to re-link `.so` files against the correct Nix store libraries.
This aligns with how authentik upstream builds (they use `uv` as their package manager).
**Why not `uv pip download` + `uv pip install --no-index`?** `uv pip download` does not exist in uv 0.9.29 (nixpkgs). And the download-only approach has further complications with sdist-only packages (psycopg-c, gssapi) that must be compiled anyway.
## What to Do
1. Create a FOD that runs `uv pip download` to fetch all Python dependencies locked by `uv.lock`
2. Create the main derivation that:
- Sets up a Python 3.14 venv via `uv`
- Installs all dependencies from the FOD (offline, `--no-index`)
- Installs the 4 in-tree packages from the monorepo source (`ak-guardian`, `django-channels-postgres`, `django-dramatiq-postgres`, `django-postgres-cache`)
- Installs authentik itself
3. Apply `substituteInPlace` patches for Nix store paths in `settings.py`, `default.yml`, `email/utils.py`, `files/backends/file.py`
4. Copy lifecycle scripts, `manage.py`, blueprints, and web assets into the output
5. Verify: `python -c "import authentik"` succeeds
1. Create the FOD (`python-deps.nix`) that runs `uv sync --frozen --no-install-project --no-install-workspace --no-dev`, then strips all Nix store references from the output
2. Create the main derivation (`authentik-django.nix`) that:
- Copies the FOD's site-packages
- Recreates venv `bin/` and `pyvenv.cfg`
- Runs `autoPatchelfHook` to restore `.so` RPATHs
- Copies 4 in-tree workspace packages directly into site-packages
- Copies `authentik/` and `lifecycle/` into site-packages
- Copies `opencontainers` from `fetchFromGitHub` into site-packages
3. Apply `substituteInPlace` patches for Nix store paths in `settings.py`, `default.yml`, `email/utils.py`
4. Copy lifecycle scripts, `manage.py`, blueprints into the output
5. Verify: `$out/bin/python3.14 -c "import authentik"` succeeds
## Key Details
@ -50,6 +52,21 @@ This aligns with how authentik upstream builds (they use `uv` as their package m
- The 4 in-tree packages are installed from monorepo source, not PyPI
- Standard `djangorestframework` 3.16.1 from PyPI (no longer forked as of 2026.2.0)
## Lessons Learned (WIP)
Build issues encountered and resolved:
| Issue | Fix |
|-------|-----|
| `pg_config` not found for psycopg-c | Use `pkgs.postgresql.pg_config` (separate derivation), not `pkgs.postgresql` |
| gssapi `gss_acquire_cred_impersonate_name` undeclared | `NIX_CFLAGS_COMPILE="-include gssapi/gssapi_ext.h"` — function is in `gssapi_ext.h`, not auto-included |
| xmlsec linker error `-lltdl` | Add `pkgs.libtool` to buildInputs (provides libltdl) |
| psycopg-c needs `libpq` | Add `pkgs.libpq` to buildInputs |
| FOD references 19 store paths | Strip with `remove-references-to`, delete `bin/` and `.pyc` files, placeholder `pyvenv.cfg` |
| Still 6 residual store refs | Need to add `glibc.dev` and other `-dev` outputs to `refTargets` list — WIP |
The `uv sync` completes in ~3.5 minutes. Reference stripping reduced 19 → 6 remaining store refs. Next iteration needs to capture all remaining dev/lib output paths in the `refTargets` list.
## Related
- [[build-authentik-from-source]] — Parent goal