July 24, 2021

deps.edn and monorepos IV

This is part of an ongoing series of blog posts about our ever-evolving use of the Clojure CLI, deps.edn, and Polylith, with our monorepo at World Singles Networks.

The Monorepo/Polylith Series

This blog post is part of an ongoing series following our experiences with our Clojure monorepo and our migration to Polylith:

  1. deps.edn and monorepos
  2. deps.edn and monorepos II
  3. deps.edn and monorepos III (Polylith)
  4. deps.edn and monorepos IV (this post)
  5. deps.edn and monorepos V (Polylith)
  6. deps.edn and monorepos VI (Polylith)
  7. deps.edn and monorepos VII (Polylith)
  8. deps.edn and monorepos VIII (Polylith)

Part IV

Since last month's post, we've created Polylith projects for each of our deployable artifacts, as well as refactoring all of our cron job tasks into a new base called batch-jobs. We now have 16 projects, 3 bases, and 23 components. This has nicely separated the actual artifacts we build from the code we use to build them, providing a clear "bill of materials" for each artifact (as a deps.edn file) and now we can build each artifact with:

cd projects/<artifact>
clojure -X:uberjar

We still have the ability to run a single REPL with all our code and tests, and we also have the ability to run incremental tests on bases, components, and projects via the poly tool. We're looking forward to having incremental testing across the whole codebase, once we have refactored everything -- but that is definitely a ways off.

A Clojure Build Script

The other big change we've made in the last month is something we've been talking about internally, on and off, for a long time: switching away from an ad hoc set of bash scripts that manage our test/build/deploy processes and instead having a single Clojure script that orchestrates all of that. We've had Clojure scripts for many parts of that pipeline for a long time but we've never made the jump to running those scripts from Clojure itself. With the knowledge that tools.build was on the way, this seems like a good time to do that last leg of the work.

We've run our database migrations via Clojure for years. Our "cold start" to stand up a dev/test environment involves two sets of database migrations, an Elastic Search setup (for indices), and a "publishing" step to take dev/test data from MySQL and propagate the appropriate pieces into Elastic Search. We've run our test suite in part and in whole using Cognitect's test-runner for a long time as well and we were very pleased to see an "exec function" entry point added recently -- we've had our own "exec function" entry point for a while that performs some test setup before invoking the test-runner so this just made our lives a bit easier.

We've been building (uber) JAR files with depstar for quite some time too, and our deployment process to our staging server was also written in Clojure, uploading JAR files to S3 buckets and then notifying our auto-deploy (bash) scripts by posting "flag" files to the servers that need to retrieve those JAR files and deploy them.

We replaced two bash scripts with a single Clojure build.clj script that can run database migrations, run tests, build uberjars, upload JAR files, and notifying the staging server. Our first run at this ended up with tools.deps.alpha and all our code on the classpath, at least for test running, which caused some interesting race conditions, due to the optional S3 transporter code in tools.deps.alpha performing asynchronous requires of some libraries that we also use in our tests (including core.async). We knew this wasn't ideal -- the core team think that running tests should be separate from all the rest and that it's OK to run multiple commands but I wanted things a bit more integrated and was willing to pay the price: as a workaround, our build script required the t.d.a S3 transporter namespace to force it to load upfront, even though we don't use any of that functionality.


And then tools.build was released on July 9th, along with enhancements to the Clojure CLI and tools.deps.alpha, and the ability to install "tools" locally, per-developer, without needing to edit your deps.edn file.

Aside: At this point, I updated both depstar and clj-new to work with the new "tools" functionality, adding :tools/usage to their deps.edn files and updating the documentation to show how to install them under this new system. I also broke depstar up into tasks so that I could expose hf.depstar.api/jar and hf.depstar.api/uber as direct, drop-in replacements for clojure.tools.build.api/jar and clojure.tools.build.api/uber -- because depstar still has a lot of functionality and options that tools.build does not yet have.

tools.build provided features that allowed us to simplify our build.clj script and also offered the possibility of running our tests in an isolated environment, without the pollution of tools.deps.alpha's many dependencies: using create-basis, java-command, and process from clojure.tools.build.api makes it fairly easy to run Clojure -main programs with command-line arguments.

Unfortunately, we relied heavily on -X execution of many of our previously scripted test/build/deploy functions and we didn't have -main programs for most of those. What we really needed was a variant of java-command that built a command-line for running "exec functions". The way this is done in the Clojure CLI is via the exec.jar that is part of its install and a clojure.run.exec namespace, which has a -main that reads the command-line arguments as EDN and then invokes the specified function with a hash map of those arguments, including :exec-fn, :exec-args, etc from the project basis under the specified aliases.

This wasn't too hard to write, but it involved taking a snapshot of clojure.run.exec under a new name since it isn't yet a stable API and isn't published as a library. You can see the approach we took in TBUILD-6 which allows us to easily run -X executions in subprocesses. Unfortunately, clojure.run.exec in exec.jar has already changed in ways that would break our workaround (hence the snapshot under a different name). It seems a shame that with all the work done to support "exec functions" as command-line entry points, tools.build doesn't support that out of the box. We are happy with our workaround though.

At this point, we had a build.clj and a :build alias and our entire CI pipeline came down to just:

clojure -T:build all-tests-ci
clojure -T:build tag-build-and-upload-all

The former is an exec function that runs our "cold start" (described above) and then runs the tests for all our subprojects, both in subprocesses, and the latter uses process to run some git commands, followed by calls to depstar as a library, and then calls to our artifact uploader. Our :build alias looks like this:

  {:paths ["."] ; required to allow -M legacy invocation
   :deps {org.clojure/clojure {:mvn/version "1.11.0-alpha1"}

          io.github.clojure/tools.build {:git/tag "v0.1.6" :git/sha "5636e61"
                                         :exclusions [org.slf4j/slf4j-nop]}
          ;; add depstar for building uberjars:
          com.github.seancorfield/depstar {:git/tag "v2.1.267" :git/sha "1a45f79"
                                           :exclusions [org.slf4j/slf4j-nop]}
          ;; and local build tools:
          worldsingles/build {:local/root "build"}
          poly/base-artifact-uploader-cli {:local/root "bases/artifact-uploader-cli"}
          poly/artifact-uploader {:local/root "components/artifact-uploader"}}
   :ns-default build}

As the comment indicates, the :paths entry is there so that we can still invoke build.clj via -M which we do to support what's left of our legacy build bash script until we retire it (which will probably happen next week). The local build subproject includes some legacy app support tasks that we run from our new build.clj script (which will soon be refactored to Polylith bases and components). The artifact-uploader is what I mentioned above, uploading JAR files to S3.

Footnote: depstar and clj-new

Already since tools.build was released, it has had several enhancement releases that add features depstar has had for a while and, talking to Alex Miller, it's likely that most (or perhaps even all) of depstar's functionality will be implemented in the built-in jar and uber tasks over time -- which makes me very happy since I will be able to direct my open source maintenance energy into other projects!

I've also observed to a few people that most of what clj-new does for internal templates (app, lib, and template) could easily be done via clojure.tools.build.api/copy-dir since it supports text substitutions. With create-basis, java-command, and process, it looks possible to reproduce most of clj-new's external template functionality as a very thin wrapper around tools.build as well. My thoughts on this are less well-formed than around depstar but my hope is that both of my libraries/tools will essentially either go away or be substantially simplified which in turn should reduce the sense of fragmentation of tools around the CLI and deps.edn and encourage more people to standardize on the tooling that the core team are carefully producing.

Tags: clojure polylith tools.build monorepo