Allow override for requesting specific worker types for Complement on command line. (#14324)

* Expose getting SYNAPSE_WORKER_TYPES from external, allowing override of workers requested.

* Add WORKER_TYPES variable option to complement.sh script that passes requested workers into start_for_complement.sh entrypoint.

* Update docs to reflect this new ability.

* Changelog

* Don't rely on soft wrapping to format long strings

Good idea dklimpel. Thanks for catching that.

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>

* Small nits just noticed in docs.

* Fixup new line in docs.

Co-authored-by: Dirk Klimpel <5740567+dklimpel@users.noreply.github.com>

4 files changed, 18 insertions, 1 deletions

diff --git a/changelog.d/14324.misc b/changelog.d/14324.misc
new file mode 100644
index 0000000000..54d8198a8f
--- /dev/null
+++ b/changelog.d/14324.misc
@@ -0,0 +1 @@
+Add override ability to `complement.sh` command line script to request certain types of workers.
diff --git a/docker/complement/conf/start_for_complement.sh b/docker/complement/conf/start_for_complement.sh
index bb85d9fed7..49d79745b0 100755
--- a/docker/complement/conf/start_for_complement.sh
+++ b/docker/complement/conf/start_for_complement.sh
@@ -45,7 +45,12 @@ esac
 
 if [[ -n "$SYNAPSE_COMPLEMENT_USE_WORKERS" ]]; then
   # Specify the workers to test with
-  export SYNAPSE_WORKER_TYPES="\
+  # Allow overriding by explicitly setting SYNAPSE_WORKER_TYPES outside, while still
+  # utilizing WORKERS=1 for backwards compatibility.
+  # -n True if the length of string is non-zero.
+  # -z True if the length of string is zero.
+  if [[ -z "$SYNAPSE_WORKER_TYPES" ]]; then
+    export SYNAPSE_WORKER_TYPES="\
       event_persister, \
       event_persister, \
       background_worker, \
@@ -61,6 +66,8 @@ if [[ -n "$SYNAPSE_COMPLEMENT_USE_WORKERS" ]]; then
       appservice, \
       pusher"
 
+  fi
+  log "Workers requested: $SYNAPSE_WORKER_TYPES"
   # Improve startup times by using a launcher based on fork()
   export SYNAPSE_USE_EXPERIMENTAL_FORKING_LAUNCHER=1
 else
diff --git a/docs/development/contributing_guide.md b/docs/development/contributing_guide.md
index 1e52f9808c..342bc1d340 100644
--- a/docs/development/contributing_guide.md
+++ b/docs/development/contributing_guide.md
@@ -324,6 +324,12 @@ The above will run a monolithic (single-process) Synapse with SQLite as the data
 
 - Passing `POSTGRES=1` as an environment variable to use the Postgres database instead.
 - Passing `WORKERS=1` as an environment variable to use a workerised setup instead. This option implies the use of Postgres.
+  - If setting `WORKERS=1`, optionally set `WORKER_TYPES=` to declare which worker
+    types you wish to test. A simple comma-delimited string containing the worker types
+    defined from the `WORKERS_CONFIG` template in
+    [here](https://github.com/matrix-org/synapse/blob/develop/docker/configure_workers_and_start.py#L54).
+    A safe example would be `WORKER_TYPES="federation_inbound, federation_sender, synchrotron"`.
+    See the [worker documentation](../workers.md) for additional information on workers.
 
 To increase the log level for the tests, set `SYNAPSE_TEST_LOG_LEVEL`, e.g:
 ```sh
diff --git a/scripts-dev/complement.sh b/scripts-dev/complement.sh
index 76c859694f..803c6ce92d 100755
--- a/scripts-dev/complement.sh
+++ b/scripts-dev/complement.sh
@@ -139,6 +139,9 @@ if [[ -n "$WORKERS" ]]; then
   # Use workers.
   export PASS_SYNAPSE_COMPLEMENT_USE_WORKERS=true
 
+  # Pass through the workers defined. If none, it will be an empty string
+  export PASS_SYNAPSE_WORKER_TYPES="$WORKER_TYPES"
+
   # Workers can only use Postgres as a database.
   export PASS_SYNAPSE_COMPLEMENT_DATABASE=postgres