Merge pull request #17 from guardian/first-server-defaulting-faq

FAQ to remind people to define both protocols

Author: johnduffell

README.md

@@ -6,6 +6,9 @@ This typically allows accessing servers via
 `service.local.dev-gutools.co.uk`, rather than a `localhost:PORT` URL,
 which among other things makes it possible to share cookies for the [pan-domain authentication](https://github.com/guardian/pan-domain-authentication).
 
+### Strange errors or behaviour
+See [troubleshooting faq](TROUBLESHOOTING.md)
+
 ### What does dev-nginx do?
 
 Installing and running dev-nginx will start an [nginx](https://nginx.org/en/) server instance locally on your machine.

TROUBLESHOOTING.md

@@ -1,5 +1,28 @@
 # Troubleshooting
 
+## Hitting one hostname actually tries to serve another
+This can happen if you don't use the standard [setup-app command](README.md#setup-app)
+
+`$ tail /usr/local/var/log/nginx/error.log`
+shows something like this
+
+`2020/04/03 13:37:13 [error] 51098#0: *5 kevent() reported that connect() failed (61: Connection refused) while connecting to upstream, client: 127.0.0.1, server: promo.thegulocal.com, request: "GET / HTTP/1.1", upstream: "http://[::1]:9500/", host: "mem.thegulocal.com"`
+
+you can see the correct host mem.thegulocal.com, but the incorrect server and port number promo.thegulocal.com and 9500.
+
+This is because if nginx can't find a matching server block for host AND protocol, it just picks the first one, which in this case is promo.  If you access with https it works fine, but be sure to define the http as well as the https in your [nginx config file](https://github.com/guardian/membership-frontend/blob/master/nginx/membership.conf) if you want the redirect to work:
+```
+server {
+  server_name mem.thegulocal.com;
+
+  location / {
+    proxy_pass http://localhost:9100/;
+      proxy_set_header Host $http_host;
+  }
+}
+```
+
+## Hash bucket size emerg
 Seeing a message such as `nginx: [emerg] could not build server_names_hash, you should increase server_names_hash_bucket_size: 64` after starting nginx 
 is a sign that an unusually long server name has been defined.
 
@@ -13,4 +36,4 @@ http {
 }
 ```
 
-See [the docs](https://nginx.org/en/docs/http/server_names.html#optimization) for more information.
+See [the docs](https://nginx.org/en/docs/http/server_names.html#optimization) for more information.