Merge pull request #3459 from opensourcerouting/feature/topotests-registry

tests/topotests: Pull docker image from registry

tests/topotests/docker/README.md

@@ -10,19 +10,15 @@ Your current user needs to have access to the Docker daemon. Alternatively
 you can run these commands as root.
 
 ```console
-make topotests-build
 make topotests
 ```
 
-The first command will build a docker image with all the dependencies needed
+This command will pull the most recent topotests image from dockerhub, compile FRR inside
-to run the topotests.
-
-The second command will spawn an instance of this image, compile FRR inside
 of it, and run the topotests.
 
 ## Advanced Usage
 
-Internally, the topotests make target uses a shell script to spawn the docker
+Internally, the topotests make target uses a shell script to pull the image and spawn the docker
 container.
 
 There are several environment variables which can be used to modify the behavior
@@ -55,3 +51,22 @@ And to compile FRR but drop into a shell instead of running pytest:
 ```console
 ./tests/topotests/docker/frr-topotests.sh /bin/bash
 ```
+
+## Development
+
+The docker image just includes all the components to run the topotests, but not the topotests
+themselves. So if you just want to write tests and don't want to make changes to the environment
+provided by the docker image. You don't need to build your own docker image if you do not want to.
+
+When developing new tests, there is one caveat though: The startup script of the container will
+run a `git-clean` on its copy of the FRR tree to avoid any pollution of the container with build
+artefacts from the host. This will also result in your newly written tests being unavailable in the
+container unless at least added to the index with `git-add`.
+
+If you do want to test changes to the docker image, you can locally build the image and run the tests
+without pulling from the registry using the following commands:
+
+```console
+make topotests-build
+TOPOTEST_PULL=0 make topotests
+```

tests/topotests/docker/frr-topotests.sh

@@ -61,6 +61,9 @@ if [[ "$1" = "-h" ]] || [[ "$1" = "--help" ]]; then
 	TOPOTEST_OPTIONS        These options are appended to the docker-run
 	                        command for starting the tests.
 
+	TOPOTEST_PULL           If set to 0, don't try to pull the most recent
+	                        version of the docker image from dockerhub.
+
 	TOPOTEST_SANITIZER      Controls whether to use the address sanitizer.
 	                        Enabled by default, set to 0 to disable.
 
@@ -132,6 +135,10 @@ if [ -z "$TOPOTEST_BUILDCACHE" ]; then
 		|| docker volume create "${TOPOTEST_BUILDCACHE}"
 fi
 
+if [ "${TOPOTEST_PULL:-1}" = "1" ]; then
+	docker pull frrouting/frr:topotests-latest
+fi
+
 set -- --rm -i \
 	-v "$TOPOTEST_LOGS:/tmp" \
 	-v "$TOPOTEST_FRR:/root/host-frr:ro" \