A bunch of random scratchings written in go.
Counter is a simple stateful webserver. It was written to demonstrate one possible use case for Checkpoint/Restore in Userspace CRIU
The CRIU website has a very useful article on integration with docker. Doesn't require that much setup, but does rely on an experimental feature that you'll have to manually enable on the docker daemon. See the article for more details!
Run make counter to build the docker image and tag it as counter:test.
docker run --name counter -p 9993:9993 counter:test
Once it's running, hit the endpoint a coupe of times to increment the counter. When you've hit your favorite number, create a checkpoint:
docker checkpoint create counter checkpoint1
This command will step through the process of creating a checkpoint for the container. More or less this seems to include:
- Seizing the processes with
ptrace() - Collecting the details from
/proc/<PID>/* - Injecting parasite code into the process, runs as a daemon in the address space of process. It essentially collects info about the types of pages that need to be written. It gets removed after usage.
- All of the required information gets written to disk and the process gets killed.
To restart the frozen container, you can run:
docker start --checkpoint checkpoint1 counter
Note that this is the most trivial example for stoping and restarting the same container, the CRIU article contains more information on using the checkpoint to start different containers.