fix(interop): only write to cache if we have credentials

For pull-requests coming from forks, we don't have access to the secrets. This is currently failing CI for all PRs from forks as docker cannot write the cache after running the tests.

Pull-Request: #4604.

.github/workflows/interop-test.yml

@@ -21,19 +21,12 @@ jobs:
 
       - uses: docker/setup-buildx-action@v3
 
-      # This uses the same S3 cache as all test-plans images. Because we use `cargo-chef` in the Dockerfile, we have a layer available with all dependencies built.
       - name: Build ${{ matrix.flavour }} image
-        run: |
-          docker buildx build \
-            --load \
-            --cache-to   type=s3,mode=max,bucket=libp2p-by-tf-aws-bootstrap,region=us-east-1,prefix=buildCache,name=${{ matrix.flavour }}-rust-libp2p-head \
-            --cache-from type=s3,mode=max,bucket=libp2p-by-tf-aws-bootstrap,region=us-east-1,prefix=buildCache,name=${{ matrix.flavour }}-rust-libp2p-head \
-            -t ${{ matrix.flavour }}-rust-libp2p-head \
-            . \
-            -f interop-tests/Dockerfile.${{ matrix.flavour }}
+        run: ./scripts/build-interop-image.sh
         env:
           AWS_ACCESS_KEY_ID: ${{ vars.TEST_PLANS_BUILD_CACHE_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.TEST_PLANS_BUILD_CACHE_KEY }}
+          FLAVOUR: ${{ matrix.flavour }}
 
       - name: Run ${{ matrix.flavour }} tests
         uses: libp2p/test-plans/.github/actions/run-interop-ping-test@master

scripts/build-interop-image.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# This uses the same S3 cache as all test-plans images. Because we use `cargo-chef` in the Dockerfile, we have a layer available with all dependencies built.
+
+CACHE_TO=""
+
+# If we have credentials, write to cache
+if [[ -n "${AWS_SECRET_ACCESS_KEY}" ]]; then
+  CACHE_TO="--cache-to   type=s3,mode=max,bucket=libp2p-by-tf-aws-bootstrap,region=us-east-1,prefix=buildCache,name=${FLAVOUR}-rust-libp2p-head"
+fi
+
+docker buildx build \
+  --load \
+  $CACHE_TO \
+  --cache-from type=s3,mode=max,bucket=libp2p-by-tf-aws-bootstrap,region=us-east-1,prefix=buildCache,name=${FLAVOUR}-rust-libp2p-head \
+  -t ${FLAVOUR}-rust-libp2p-head \
+  . \
+  -f interop-tests/Dockerfile.${FLAVOUR}