fix: expose udp port in dockerfile

I think that could be the reason why the application does not work on
the Azure Container Instance.

Dockerfile

@@ -45,6 +45,6 @@ COPY --from=builder --chown=$RUN_AS_USER \
   /app/torrust-tracker
 RUN chown -R $RUN_AS_USER:$RUN_AS_USER /app
 USER $RUN_AS_USER:$RUN_AS_USER
-EXPOSE 6969
+EXPOSE 6969/udp
 EXPOSE 1212
 ENTRYPOINT ["/app/torrust-tracker"]

docker/README.md

@@ -54,7 +54,7 @@ And finally, you can run the container:
 
 ```s
 docker run \
-    --publish 80:80/udp \
+    --publish 6969:6969/udp \
     --publish 1212:1212 \
     --volume torrustracker/test-volume:/app/storage \
     registry.hub.docker.com/josecelano/torrust-tracker:0.4.0
@@ -65,25 +65,25 @@ Detach from container logs when the container starts. By default, the command li
 ```s
 docker run \
     --detach
-    --publish 80:80/udp \
+    --publish 6969:6969/udp \
     --publish 1212:1212 \
     --volume torrustracker/test-volume:/app/storage \
-    registry.hub.docker.com/josecelano/torrust-tracker:0.4.0
+    registry.hub.docker.com/josecelano/torrust-tracker:0.5.0
 ```
 
 You should see something like this:
 
 ```s
 $ docker run \ \
-    --publish 80:80/udp \
+    --publish 6969:6969/udp \
     --publish 1212:1212 \
     --volume torrustracker/test-volume:/app/storage \
-    registry.hub.docker.com/josecelano/torrust-tracker:0.4.0
+    registry.hub.docker.com/josecelano/torrust-tracker:0.5.0
 [+] Running 2/2
  ⠿ Group intelligent-hawking  Created                                                                                                                                                                    5.0s
  ⠿ intelligent-hawking        Created                                                                                                                                                                   41.7s
 2022-12-08T18:39:19.697869300+00:00 [torrust_tracker::logging][INFO] logging initialized.
-2022-12-08T18:39:19.712651100+00:00 [torrust_tracker::jobs::udp_tracker][INFO] Starting UDP server on: 0.0.0.0:80
+2022-12-08T18:39:19.712651100+00:00 [torrust_tracker::jobs::udp_tracker][INFO] Starting UDP server on: 0.0.0.0:6969
 2022-12-08T18:39:19.712792700+00:00 [torrust_tracker::jobs::tracker_api][INFO] Starting Torrust API server on: 0.0.0.0:1212
 2022-12-08T18:39:19.725124+00:00 [torrust_tracker::jobs::tracker_api][INFO] Torrust API server started
 ```
@@ -93,10 +93,10 @@ You can see the container with:
 ```s
 $ docker ps
 CONTAINER ID          IMAGE                                                      COMMAND             STATUS              PORTS
-intelligent-hawking   registry.hub.docker.com/josecelano/torrust-tracker:0.4.0                       Running             4.236.213.57:80->80/udp, 4.236.213.57:1212->1212/tcp
+intelligent-hawking   registry.hub.docker.com/josecelano/torrust-tracker:0.5.0                       Running             4.236.213.57:6969->6969/udp, 4.236.213.57:1212->1212/tcp
 ```
 
-After a while, you can use the tracker API `http://4.236.213.57:1212/api/stats?token=MyAccessToken` and the UDP tracker with your BitTorrent client using this tracker announce URL `udp://4.236.213.57:80/announce`.
+After a while, you can use the tracker API `http://4.236.213.57:1212/api/stats?token=MyAccessToken` and the UDP tracker with your BitTorrent client using this tracker announce URL `udp://4.236.213.57:6969/announce`.
 
 > NOTES:
 >
@@ -105,6 +105,7 @@ After a while, you can use the tracker API `http://4.236.213.57:1212/api/stats?t
 > - [Azure file share volume mount requires the Linux container run as root](https://learn.microsoft.com/en-us/azure/container-instances/container-instances-volume-azure-files#limitations).
 > - It can take some minutes until the public IP for the ACI container is available.
 > - You can use the Azure web UI to download files from the storage. For example, the SQLite database.
+> - [It seems you can only expose web interfaces on port 80 on Azure Container Instances](https://stackoverflow.com/a/56768087/3012842). Not official documentation!
 
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