Solver Service

A standalone, OCurrent service for solving opam dependencies extracted and modified from OCaml-CI. This repostory contains:

• api: The Capnp solver service API, the defines the format for sending requests and receiving responses from a service.
• service: The core functionality of completing a solver request using opam-0install is contained here.
• worker: An OCluster worker that can solve requests being submitted to OCluster as a custom job specification.
• bin: Binaries for running as either a stand-alone service or as an OCluster worker.

Example

A solver service

The ./examples directory contains a small CLI tool for testing the solver service over a TCP connection. It requires a package name and version to solve for (note it will use opam to fetch the opam file information). To test it, you first must install and run the solver service.

$ mkdir capnp-secrets
$ dune exec -- solver-service run-service \
    --cache-dir=./cache \
    --capnp-secret-key-file=server.pem \
    --capnp-listen-address=tcp:127.0.0.1:7000 \
    --cap-file=./capnp-secrets/solver.cap
Wrote solver service's address to "./capnp-secrets/solver.cap"

Then run the example client to test it:

$ dune exec -- ./examples/main.exe --package=yaml --version=3.0.0 ./capnp-secrets/solver.cap

For a more thorough test, you can use the stress tester:

$ dune exec -- ./stress/stress.exe service ./capnp-secrets/solver.cap --count=10
Solved warm-up requests in: 9.85s
Running another 10 solves...
10/10 complete
Solved 10 requests in 4.79s (0.48s/iter)

An OCluster worker

The solver worker can join an existing pool on a scheduler and solve request jobs sent as a custom job type. The example submit.ml will send such a job to a scheduler (you need to supply the submission cap file).

To try this example locally, first get the scheduler up and running.

$ ocluster-scheduler --capnp-secret-key-file=capnp-secrets/scheduler-key.cap --capnp-listen-address=tcp:127.0.0.1:9000 --pools=solver --state-dir=var --default-clients=demo

This will write a submit-demo.cap file into capnp-secrets.

Now, we need to connect our solver worker to the pool. In a new terminal connect the worker using the pool registration cap file.

$ dune exec -- solver-service run-cluster \
    --connect=capnp-secrets/pool-solver.cap \
    --name=solver-1 \
    --cache-dir=./cache \
    --verbosity=info

With this running we can use the example submission pipeline to solve the dependencies for the obuilder repository on Github.

You should then be able to watch the pipeline in action at http://localhost:8080.

$ dune exec -- examples/submit.exe --submission-service=capnp-secrets/submit-demo.cap -v

You can also run the stress tests against the cluster:

$ dune exec -- ./stress/stress.exe cluster ./capnp-secrets/submit-demo.cap --count=10
Solved warm-up requests in: 10.01s
Running another 10 solves...
10/10 complete
Solved 10 requests in 5.19s (0.52s/iter)

A solver worker by docker-compose

Start a solver-worker connected to a scheduler.

$ docker-compose -f docker-compose.yml up

Get the Mountpoint by inspecting the capnp-secrets volume.

$ docker volume inspect solver-service_capnp-secrets
[
    {
        "CreatedAt": "2023-06-02T17:00:23+02:00",
        "Driver": "local",
        "Labels": {
            "com.docker.compose.project": "solver-service",
            "com.docker.compose.version": "1.29.2",
            "com.docker.compose.volume": "capnp-secrets"
        },
        "Mountpoint": "/var/lib/docker/volumes/solver-service_capnp-secrets/_data",
        "Name": "solver-service_capnp-secrets",
        "Options": null,
        "Scope": "local"
    }
]

Be root to get the submit-docker.cap file from the Mountpoint path:

$ mkdir capnp-secrets
$ sudo cat /var/lib/docker/volumes/solver-service_capnp-secrets/_data/submit-docker.cap > ./capnp-secrets/submit-docker.cap

To reach the scheduler, you can either edit the .cap file to replace scheduler with 127.0.0.1, or you can add scheduler to your /etc/hosts file:

$ cat /etc/hosts
127.0.0.1   localhost
127.0.0.1   scheduler

We can use the submit-docker.cap file to submit jobs:

$ dune exec -- ./stress/stress.exe cluster ./capnp-secrets/submit-docker.cap --count=10
Solved warm-up requests in: 23.68s
Running another 10 solves...
10/10 complete
Solved 10 requests in 17.85s (1.79s/iter) (8.96 solves/s)

Testing

The test directly contains various tests of the solver. Running dune test runs them and compares the output with the good copy in ./test/test.expected.

For more realistic testing, the stress tester can also run in local mode to run the solver in-process:

$ dune exec -- ./stress/stress.exe local --cache-dir=./cache --count=10
Solved warm-up requests in: 21.46s
Running another 10 solves...
10/10 complete
Solved 10 requests in 17.87s (1.79s/iter) (8.95 solves/s)