Fix nginx when some services are disabled

nginx tries to resolve everything at startup, which doesn't work
if some of the services aren't present.

we instead generate the config file from a passed in env var, so that only
enabled services are present.

docker-compose.jsonnet

@@ -208,9 +208,25 @@
     },
 
     [if $.enabled.nginx then "nginx"]: {
+      # mapping of services to internal ports for nginx to forward
+      local forward_ports = {
+        restreamer: 8000,
+        downloader: 8001,
+        backfiller: 8002,
+        cutter: 8003,
+        thrimshim: 8004,
+        sheetsync: 8005,
+      },
       image: "quay.io/ekimekim/wubloader-nginx:%s" % $.image_tag,
       restart: "on-failure",
       [if "nginx" in $.ports then "ports"]: ["%s:80" % $.ports.nginx],
+      environment: {
+        SERVICES: std.join("\n", [
+          "%s %s" % [service, forward_ports[service]]
+          for service in std.objectFields(forward_ports)
+          if service in $.enabled && $.enabled[service]
+        ]),
+      },
     },
 
     [if $.enabled.postgres then "postgres"]: {

nginx/Dockerfile

@@ -1,3 +1,4 @@
 # nginx container contains config that exposes all the various services metrics
 FROM nginx:latest
-ADD nginx/nginx.conf /etc/nginx/nginx.conf
+ADD nginx/generate-config /
+ENTRYPOINT ["/bin/sh", "-c", "/generate-config && nginx -g \"daemon off;\""]

nginx/generate-config

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+# This script expects a mapping of services and ports in the SERVICES env var,
+# with one line per service containing "NAME PORT".
+
+generate_location() {
+	# generate_location PATH URL
+	echo -e "\t\tlocation $1 { proxy_pass $2; }"
+}
+
+LOCATIONS=$(
+	echo "$SERVICES" | while read name port; do
+		# restreamer is the catch-all
+		[ "$name" == "restreamer" ] && generate_location / "http://restreamer:$port"
+		# thrimshim takes any calls to thrimshim/
+		[ "$name" == "thrimshim" ] && generate_location /thrimshim "http://thrimshim:$port"
+		# all services have metrics under /metrics/SERVICE
+		generate_location "/metrics/$name" "http://$name:$port/metrics"
+	done
+)
+
+cat > /etc/nginx/nginx.conf <<EOF
+worker_processes 1;
+
+events {
+	worker_connections 1024;
+}
+
+http {
+	server {
+		listen 80;
+$LOCATIONS
+	}
+}
+EOF

nginx/nginx.conf

@@ -1,37 +0,0 @@
-
-worker_processes 1;
-
-events {
-	worker_connections 1024;
-}
-
-http {
-	server {
-		listen 80;
-		location / {
-			proxy_pass http://restreamer:8000;
-		}
-		location /thrimshim {
-			proxy_pass http://thrimshim:8004;
-		}
-		# Restreamer metrics would be available regardless, this is just for consistency
-		location /metrics/restreamer {
-			proxy_pass http://restreamer:8000/metrics;
-		}
-		location /metrics/downloader {
-			proxy_pass http://downloader:8001/metrics;
-		}
-		location /metrics/backfiller {
-			proxy_pass http://backfiller:8002/metrics;
-		}
-		location /metrics/cutter {
-			proxy_pass http://cutter:8003/metrics;
-		}
-		location /metrics/thrimshim {
-			proxy_pass http://thrimshim:8004/metrics;
-		}
-		location /metrics/sheetsync {
-			proxy_pass http://sheetsync:8005/metrics;
-		}
-	}
-}