Dockerfile: build both RHEL7 and RHEL8 shims

Since the shim (ovn-k8s-cni-overlay) gets copied to the host OS
and executed in the host mount namespace by CRIO/Multus it needs
to be runtime compatible with the host OS. Running a RHEL8-built
shim on a RHEL7 system doesn't work due to different shared library
dependencies between the two OS versions.

This wasn't a problem before because CGO_ENABLED=0 which essentially
statically linked everything into the binary. But since we actually
need CGO_ENABLED=1 (which ART forces on "official" builds anyway)
to ensure we use OpenSSL's crypto for FIPS compliance, we run into
the OS version problem with our binaries since they are really
always built with CGO_ENABLED=1 anyway.

So... build two separate versions of ovn-kubernetes in different
layers, and copy the RHEL7 shim into a special location where our
container startup scripts can find it.

Signed-off-by: Jaime Caamaño Ruiz <jcaamano@redhat.com>
(cherry picked from commit 932ef31)
(cherry picked from commit 20f8d23)

Dockerfile

@@ -9,14 +9,18 @@
 # are built in this Dockerfile and included in the image (instead of the rpm)
 #
 
+# Build RHEL-8 binaries
 FROM registry.ci.openshift.org/ocp/builder:rhel-8-golang-1.15-openshift-4.7 AS builder
-
 WORKDIR /go/src/github.com/openshift/ovn-kubernetes
 COPY . .
+RUN cd go-controller; CGO_ENABLED=1 make
+RUN cd go-controller; CGO_ENABLED=1 make windows
 
-# build the binaries
-RUN cd go-controller; CGO_ENABLED=0 make
-RUN cd go-controller; CGO_ENABLED=0 make windows
+# Build RHEL-7 binaries
+FROM registry.ci.openshift.org/ocp/builder:rhel-7-golang-1.15-openshift-4.7 AS rhel7
+WORKDIR /go/src/github.com/openshift/ovn-kubernetes
+COPY . .
+RUN cd go-controller; CGO_ENABLED=1 make
 
 FROM registry.ci.openshift.org/ocp/4.7:cli AS cli
 
@@ -62,6 +66,12 @@ COPY --from=builder /go/src/github.com/openshift/ovn-kubernetes/go-controller/_o
 COPY --from=builder /go/src/github.com/openshift/ovn-kubernetes/go-controller/_output/go/bin/ovndbchecker /usr/bin/
 COPY --from=builder /go/src/github.com/openshift/ovn-kubernetes/go-controller/_output/go/bin/ovnkube-trace /usr/bin/
 
+# Copy RHEL-8 and RHEL-7 shim binaries where the CNO's ovnkube-node container startup script can find them
+RUN mkdir -p /usr/libexec/cni/rhel8
+COPY --from=builder /go/src/github.com/openshift/ovn-kubernetes/go-controller/_output/go/bin/ovn-k8s-cni-overlay /usr/libexec/cni/rhel8/
+RUN mkdir -p /usr/libexec/cni/rhel7
+COPY --from=rhel7 /go/src/github.com/openshift/ovn-kubernetes/go-controller/_output/go/bin/ovn-k8s-cni-overlay /usr/libexec/cni/rhel7/
+
 COPY --from=cli /usr/bin/oc /usr/bin/
 RUN ln -s /usr/bin/oc /usr/bin/kubectl
 RUN stat /usr/bin/oc