Merge pull request #2647 from crazy-max/docs-cni

docs: custom image with cni networking

docs/cni-networking.md

@@ -0,0 +1,30 @@
+# CNI networking
+
+It can be useful to use a bridge network for your builder if for example you
+encounter a network port contention during multiple builds. If you're using
+the BuildKit image, CNI is not [(yet)](https://github.com/moby/buildkit/issues/28)
+available in it.
+
+But you can create your own BuildKit image with CNI support:
+
+```dockerfile
+ARG BUILDKIT_VERSION=v0.9.3
+ARG CNI_VERSION=v1.0.1
+
+FROM --platform=$BUILDPLATFORM alpine AS cni-plugins
+RUN apk add --no-cache curl
+ARG CNI_VERSION
+ARG TARGETOS
+ARG TARGETARCH
+WORKDIR /opt/cni/bin
+RUN curl -Ls https://github.com/containernetworking/plugins/releases/download/$CNI_VERSION/cni-plugins-$TARGETOS-$TARGETARCH-$CNI_VERSION.tgz | tar xzv
+
+FROM moby/buildkit:${BUILDKIT_VERSION}
+ARG BUILDKIT_VERSION
+RUN apk add --no-cache iptables
+COPY --from=cni-plugins /opt/cni/bin /opt/cni/bin
+ADD https://raw.githubusercontent.com/moby/buildkit/${BUILDKIT_VERSION}/hack/fixtures/cni.json /etc/buildkit/cni.json
+```
+
+Here we use the [CNI config for integration tests in BuildKit](../hack/fixtures/cni.json),
+but feel free to use your own config.