Sometimes we want to be able to run some debug code within a stack running in our staging test environment.

For example, changes to the nr-launcher component or any of the other components that run within the stack.

This guide shows a simple way to do that without having to rebuild the container from scratch each time.

This will require:

1. Docker
2. A container registry you can push images to. For example, a free DockerHub account where you can push images

#  Creating a debug container

Pick an existing container image to use as your starting point. For example, flowfuse/node-red:2.5.0-4.0.x contains nr-launcher@2.5.0 and the latest Node-RED 4.x release.

Note: our staging environments requires arm64 based containers. The following instructions work for Macs (with M1/M2) - additional steps may be needed for other OS; please contribute them if you know them.

Use the following command to open a shell into the container:

docker run -it --entrypoint /bin/bash flowfuse/node-red:2.5.0-4.0.x

The prompt will then look like this:

e8dcd669ea4c:/usr/src/flowforge-nr-launcher$

Take a note of the e8dcd669ea4c - this is the id of the container instance you have created.

The following directories are probably of interest:

• /usr/src/flowforge-nr-launcher - contains the nr-launcher code and its dependencies
• /usr/src/node-red - contains the node-red code

Using vi, you can edit the files to make the changes you want and when you're done, exit the shell.

Having made the changes, use docker commit to create a new container image. The command requires the id of the container you've just edited and the tag for the container. It also needs to restore the entrypoint configuration back to the default.

docker commit \
  --change='ENTRYPOINT ["./node_modules/.bin/flowfuse-node-red", "-p", "2880", "-n", "/usr/src/node-red"]' \
  e8dcd669ea4c \
  knolleary/ff-debug:debug-1

Finally, you can push the new container to your container registry.

docker push knolleary/ff-debug:debug-1

#  Using the container in FlowFuse

Debug containers should only be used in pre-staging/staging environments. Do not add to production.

Once pushed, you can create a custom stack in the FlowFuse admin section and give it the location of your container.

#  Iterating

If you find you want to add some more debug, repeat the process, however use your existing image as the starting point:

docker run -it --entrypoint /bin/bash knolleary/ff-debug:debug-1

Be sure to increment the number in the image name (debug-2) when you commit and push the new container.

#  Tidying up

Remember to delete your instances/stacks once you're done, as well as all of the local docker images and containers that have been created along the way.