Add a dockerfile for running a set of Synapse worker processes (#9162)

This PR adds a Dockerfile and some supporting files to the `docker/` directory. The Dockerfile's intention is to spin up a container with:

* A Synapse main process.
* Any desired worker processes, defined by a `SYNAPSE_WORKERS` environment variable supplied at runtime.
* A redis for worker communication.
* A nginx for routing traffic.
* A supervisord to start all worker processes and monitor them if any go down.

Note that **this is not currently intended to be used in production**. If you'd like to use Synapse workers with Docker, instead make use of the official image, with one worker per container. The purpose of this dockerfile is currently to allow testing Synapse in worker mode with the [Complement](https://github.com/matrix-org/complement/) test suite.

`configure_workers_and_start.py` is where most of the magic happens in this PR. It reads from environment variables (documented in the file) and creates all necessary config files for the processes. It is the entrypoint of the Dockerfile, and thus is run any time the docker container is spun up, recreating all config files in case you want to use a different set of workers. One can specify which workers they'd like to use by setting the `SYNAPSE_WORKERS` environment variable (as a comma-separated list of arbitrary worker names) or by setting it to `*` for all worker processes. We will be using the latter in CI.

Huge thanks to @MatMaul for helping get this all working :tada: This PR is paired with its equivalent on the Complement side: https://github.com/matrix-org/complement/pull/62.

Note, for the purpose of testing this PR before it's merged: You'll need to (re)build the base Synapse docker image for everything to work (`matrixdotorg/synapse:latest`). Then build the worker-based docker image on top (`matrixdotorg/synapse:workers`). 

2 files changed, 34 insertions, 2 deletions

diff --git a/docker/conf/homeserver.yaml b/docker/conf/homeserver.yaml
index a792899540..2b23d7f428 100644
--- a/docker/conf/homeserver.yaml
+++ b/docker/conf/homeserver.yaml
@@ -40,7 +40,9 @@ listeners:
         compress: false
   {% endif %}
 
-  - port: 8008
+  # Allow configuring in case we want to reverse proxy 8008
+  # using another process in the same container
+  - port: {{ SYNAPSE_HTTP_PORT or 8008 }}
     tls: false
     bind_addresses: ['::']
     type: http
diff --git a/docker/conf/log.config b/docker/conf/log.config
index 491bbcc87a..34572bc0f3 100644
--- a/docker/conf/log.config
+++ b/docker/conf/log.config
@@ -2,9 +2,34 @@ version: 1
 
 formatters:
   precise:
-   format: '%(asctime)s - %(name)s - %(lineno)d - %(levelname)s - %(request)s - %(message)s'
+{% if worker_name %}
+    format: '%(asctime)s - worker:{{ worker_name }} - %(name)s - %(lineno)d - %(levelname)s - %(request)s - %(message)s'
+{% else %}
+    format: '%(asctime)s - %(name)s - %(lineno)d - %(levelname)s - %(request)s - %(message)s'
+{% endif %}
 
 handlers:
+  file:
+    class: logging.handlers.TimedRotatingFileHandler
+    formatter: precise
+    filename: {{ LOG_FILE_PATH or "homeserver.log" }}
+    when: "midnight"
+    backupCount: 6  # Does not include the current log file.
+    encoding: utf8
+
+  # Default to buffering writes to log file for efficiency. This means that
+  # there will be a delay for INFO/DEBUG logs to get written, but WARNING/ERROR
+  # logs will still be flushed immediately.
+  buffer:
+    class: logging.handlers.MemoryHandler
+    target: file
+    # The capacity is the number of log lines that are buffered before
+    # being written to disk. Increasing this will lead to better
+    # performance, at the expensive of it taking longer for log lines to
+    # be written to disk.
+    capacity: 10
+    flushLevel: 30  # Flush for WARNING logs as well
+
   console:
     class: logging.StreamHandler
     formatter: precise
@@ -17,6 +42,11 @@ loggers:
 
 root:
     level: {{ SYNAPSE_LOG_LEVEL or "INFO" }}
+
+{% if LOG_FILE_PATH %}
+    handlers: [console, buffer]
+{% else %}
     handlers: [console]
+{% endif %}
 
 disable_existing_loggers: false