.github/workflows: prebuilt integration test artifacts (#2954)

This PR restructures the integration tests and prebuilds all common assets used in all tests:

Headscale and Tailscale HEAD image
hi binary that is used to run tests
go cache is warmed up for compilation of the test
This essentially means we spend 6-10 minutes building assets before any tests starts, when that is done, all tests can just sprint through.

It looks like we are saving 3-9 minutes per test, and since we are limited to running max 20 concurrent tests across the repo, that means we had a lot of double work.

There is currently 113 checks, so we have to do five runs of 20, and the saving should be quite noticeable! I think the "worst case" saving would be 20+min and "best case" probably towards an hour.

.github/workflows/integration-test-template.yml

@@ -28,23 +28,12 @@ jobs:
       # that triggered the build.
       HAS_TAILSCALE_SECRET: ${{ secrets.TS_OAUTH_CLIENT_ID }}
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with:
           fetch-depth: 2
-      - name: Get changed files
-        id: changed-files
-        uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3.0.2
-        with:
-          filters: |
-            files:
-              - '*.nix'
-              - 'go.*'
-              - '**/*.go'
-              - 'integration_test/'
-              - 'config-example.yaml'
       - name: Tailscale
         if: ${{ env.HAS_TAILSCALE_SECRET }}
-        uses: tailscale/github-action@6986d2c82a91fbac2949fe01f5bab95cf21b5102 # v3.2.2
+        uses: tailscale/github-action@a392da0a182bba0e9613b6243ebd69529b1878aa # v4.1.0
         with:
           oauth-client-id: ${{ secrets.TS_OAUTH_CLIENT_ID }}
           oauth-secret: ${{ secrets.TS_OAUTH_SECRET }}
@@ -52,28 +41,62 @@ jobs:
       - name: Setup SSH server for Actor
         if: ${{ env.HAS_TAILSCALE_SECRET }}
         uses: alexellis/setup-sshd-actor@master
-      - uses: nixbuild/nix-quick-install-action@889f3180bb5f064ee9e3201428d04ae9e41d54ad # v31
-        if: steps.changed-files.outputs.files == 'true'
-      - uses: nix-community/cache-nix-action@135667ec418502fa5a3598af6fb9eb733888ce6a # v6.1.3
-        if: steps.changed-files.outputs.files == 'true'
+      - name: Download headscale image
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
-          primary-key:
-            nix-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('**/*.nix',
-            '**/flake.lock') }}
-          restore-prefixes-first-match: nix-${{ runner.os }}-${{ runner.arch }}
+          name: headscale-image
+          path: /tmp/artifacts
+      - name: Download tailscale HEAD image
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
+        with:
+          name: tailscale-head-image
+          path: /tmp/artifacts
+      - name: Download hi binary
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
+        with:
+          name: hi-binary
+          path: /tmp/artifacts
+      - name: Download Go cache
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
+        with:
+          name: go-cache
+          path: /tmp/artifacts
+      - name: Download postgres image
+        if: ${{ inputs.postgres_flag == '--postgres=1' }}
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
+        with:
+          name: postgres-image
+          path: /tmp/artifacts
+      - name: Load Docker images, Go cache, and prepare binary
+        run: |
+          gunzip -c /tmp/artifacts/headscale-image.tar.gz | docker load
+          gunzip -c /tmp/artifacts/tailscale-head-image.tar.gz | docker load
+          if [ -f /tmp/artifacts/postgres-image.tar.gz ]; then
+            gunzip -c /tmp/artifacts/postgres-image.tar.gz | docker load
+          fi
+          chmod +x /tmp/artifacts/hi
+          docker images
+          # Extract Go cache to host directories for bind mounting
+          mkdir -p /tmp/go-cache
+          tar -xzf /tmp/artifacts/go-cache.tar.gz -C /tmp/go-cache
+          ls -la /tmp/go-cache/ /tmp/go-cache/.cache/
       - name: Run Integration Test
-        if: always() && steps.changed-files.outputs.files == 'true'
-        run:
-          nix develop --command -- hi run --stats --ts-memory-limit=300 --hs-memory-limit=1500 "^${{ inputs.test }}$" \
+        env:
+          HEADSCALE_INTEGRATION_HEADSCALE_IMAGE: headscale:${{ github.sha }}
+          HEADSCALE_INTEGRATION_TAILSCALE_IMAGE: tailscale-head:${{ github.sha }}
+          HEADSCALE_INTEGRATION_POSTGRES_IMAGE: ${{ inputs.postgres_flag == '--postgres=1' && format('postgres:{0}', github.sha) || '' }}
+          HEADSCALE_INTEGRATION_GO_CACHE: /tmp/go-cache/go
+          HEADSCALE_INTEGRATION_GO_BUILD_CACHE: /tmp/go-cache/.cache/go-build
+        run: /tmp/artifacts/hi run --stats --ts-memory-limit=300 --hs-memory-limit=1500 "^${{ inputs.test }}$" \
           --timeout=120m \
           ${{ inputs.postgres_flag }}
-      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
-        if: always() && steps.changed-files.outputs.files == 'true'
+      - uses: actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4 # v5.0.0
+        if: always()
         with:
           name: ${{ inputs.database_name }}-${{ inputs.test }}-logs
           path: "control_logs/*/*.log"
-      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
-        if: always() && steps.changed-files.outputs.files == 'true'
+      - uses: actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4 # v5.0.0
+        if: always()
         with:
           name: ${{ inputs.database_name }}-${{ inputs.test }}-artifacts
           path: control_logs/