Add OpenTracing documentation (#1345)

* Add OpenTracing documentation

Closes #274

* Reshuffle

* Update setup.md

3 files changed, 49 insertions, 0 deletions

diff --git a/docs/tracing/jaeger.png b/docs/tracing/jaeger.png
new file mode 100644
index 00000000..8b1e61fe
--- /dev/null
+++ b/docs/tracing/jaeger.png
diff --git a/docs/opentracing.md b/docs/tracing/opentracing.md
index a2110bc0..a2110bc0 100644
--- a/docs/opentracing.md
+++ b/docs/tracing/opentracing.md
diff --git a/docs/tracing/setup.md b/docs/tracing/setup.md
new file mode 100644
index 00000000..2cab4d1e
--- /dev/null
+++ b/docs/tracing/setup.md
@@ -0,0 +1,49 @@
+## OpenTracing Setup
+
+![Trace when sending an event into a room](/docs/tracing/jaeger.png)
+
+Dendrite uses [Jaeger](https://www.jaegertracing.io/) for tracing between microservices.
+Tracing shows the nesting of logical spans which provides visibility on how the microservices interact.
+This document explains how to set up Jaeger locally on a single machine.
+
+### Set up the Jaeger backend
+
+The [easiest way](https://www.jaegertracing.io/docs/1.18/getting-started/) is to use the all-in-one Docker image:
+```
+$ docker run -d --name jaeger \
+  -e COLLECTOR_ZIPKIN_HTTP_PORT=9411 \
+  -p 5775:5775/udp \
+  -p 6831:6831/udp \
+  -p 6832:6832/udp \
+  -p 5778:5778 \
+  -p 16686:16686 \
+  -p 14268:14268 \
+  -p 14250:14250 \
+  -p 9411:9411 \
+  jaegertracing/all-in-one:1.18
+```
+
+### Configuring Dendrite to talk to Jaeger
+
+Modify your config to look like: (this will send every single span to Jaeger which will be slow on large instances, but for local testing it's fine)
+```
+tracing:
+  enabled: true
+  jaeger:
+    serviceName: "dendrite"
+    disabled: false
+    rpc_metrics: true
+    tags: []
+    sampler:
+      type: const
+      param: 1
+```
+
+then run the monolith server with `--api true` to use polylith components which do tracing spans:
+```
+$ ./dendrite-monolith-server --tls-cert server.crt --tls-key server.key --config dendrite.yaml --api true
+```
+
+### Checking traces
+
+Visit http://localhost:16686 to see traces under `DendriteMonolith`.