chore(README): add docker command for specifying custom port

Also properly handle SIGTERM/SIGINT events and stop the service gracefully. This is useful for those running the docker container and want to stop the service via normal commands.

README.md

@@ -32,9 +32,11 @@ Build and run the container:
 
 ```shell
 docker build --build-arg NODE_VERSION=$(cat .nvmrc |cut -c2-8) --build-arg NODE_VERSION_SHORT=$(cat .nvmrc |cut -c2-3) . -t arns-service
-docker run -p 3000:3000 arns-service
+docker run -e PORT=3000 -p 3000:3000 arns-service
 ```
 
+You can run on a different port by changing the `-e PORT=3000 -p 3000:3000` to `-e PORT=4000 -p 4000:4000`, for example.
+
 ## Warp
 
 The service leverages `warp-sdk` to retrieve, evaluate and cache contract state. To request a contract state, run:

src/app.ts

@@ -52,6 +52,16 @@ process.on('uncaughtException', (err) => {
   errorCounter.inc();
 });
 
+process.on('SIGTERM', () => {
+  logger.info('SIGTERM received, exiting...');
+  process.exit(0);
+});
+
+process.on('SIGINT', () => {
+  logger.info('SIGINT received, exiting...');
+  process.exit(0);
+});
+
 const serverConfigs = {
   port: +(process.env.PORT || 3000),
   keepAliveTimeout: 120_000, // two minute timeout for connections