Add Nginx fallback

When developing multiple services that depends on other service, it’s comfortable to have a dev environment. I usually have a docker-compose file that mount a local environment. However, I do not want to mount the whole ecosystem locally, just the services I’m currently developing.

By using Nginx, it’s possible to configure a fallback in case the local service is not up.

Here an example of the nginx.conf file that redirect HTTP to HTTPS and fallback to a dev environment service if my local service is not up:

user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
  worker_connections 1024;
}

http {
  log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
  '$status $body_bytes_sent "$http_referer" '
  '"$http_user_agent" "$http_x_forwarded_for"';

  access_log  /var/log/nginx/access.log  main;

  sendfile        on;

  server {
    listen 80 default_server;
   	listen [::]:80 default_server;
   	server_name localhost;
    # redirect HTTP to HTTPS
   	return 301 https://$host$request_uri;
  }

  server {
    listen 443          ssl;
    server_name         localhost;
    ssl_certificate     /etc/nginx/certificates/localhost.crt;
    ssl_certificate_key /etc/nginx/certificates/localhost.key;
    ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers         HIGH:!aNULL:!MD5;

    proxy_set_header Host $host;
    proxy_set_header X-Real-Ip $remote_addr;
    proxy_set_header X-Forwarded-For $remote_addr;
    proxy_set_header X-Forwarded-Proto $scheme;

    location / {
      root    /usr/share/nginx/html;
      index   index.html index.htm;
    }

    location /foobar {
      # Reverse proxy to local service
      proxy_pass http://localhost:8080;
      # if local service is not up, then use the one from the dev environment
      proxy_intercept_errors on;
      error_page 404 502 503 504 = @fallback;
    }

    location @fallback {
      # dev environment hostname
      proxy_set_header Host fallback.dev;
      proxy_pass https://fallback.dev;
    }
  }
}

graph LR;
  ST[Start] --> OP[curl -L http://localhost/foobar]
  OP --> COND{Local service up?}
  COND -->|Yes| L[Proxy to http://localhost:8080/foobar]
  COND -->|No| F[Proxy to https://fallback.dev/foobar]
  L --> E[End]
  F --> E[End]

References

• https://stackoverflow.com/questions/55764444/nginx-fallback-to-try-files-when-proxy-pass-fails-requires-unusual-config