feat: add backends config option for nginx

[AaronFeledy]

Summary

Adds a backends config option to the nginx service, allowing users to declare an array of upstream Lando services that nginx depends on and can proxy to.

Closes #5

The Problem

When multiple PHP services use via: nginx, they all get the same fpm network alias. Nginx can't distinguish which PHP-FPM backend belongs to which nginx instance, causing round-robin chaos.

The Solution

A new backends array config:

services:
  frontend:
    type: nginx
    backends:
      - backend1
      - backend2

This will:

1. Add Docker depends_on for the listed services (ensuring startup order)
2. Allow the vhost config to reference backends by their service name (Docker hostname)
3. Not break any existing configs (backwards compatible — defaults to empty array)

Status

• Leia test example added (examples/backends/)
• CI workflow updated
• Builder implementation (next step — waiting for tests to fail first, TDD style)

---

Note

Medium Risk
Moderate risk because it changes how nginx services are rendered into Docker Compose (adds depends_on and env vars), which could affect startup behavior for users who adopt the new option.

Overview
Adds a new backends config option to the nginx service builder; when set, it generates Docker depends_on entries for the named services and exports LANDO_NGINX_BACKENDS into the container environment for template/vhost use.

Introduces a new examples/backends Leia test fixture (frontend proxying to two nginx backends) and wires it into the PR GitHub Actions matrix so the new behavior is exercised in CI.

^{Written by Cursor Bugbot for commit 06a5726. This will update automatically on new commits. Configure here.}

[netlify]

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Name	Link
🔨 Latest commit	06a5726
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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is ON. A Cloud Agent has been kicked off to fix the reported issue.}

[cursor]

Bugbot Autofix prepared fixes for 1 of the 1 bugs found in the latest run.

• ✅ Fixed: CI tests will fail without builder backends implementation
  • Added backends configuration support to nginx builder by initializing backends as empty array in config and generating depends_on entries when backends are specified.

Or push these changes by commenting:

@cursor push 9ee8a58b87

Preview (9ee8a58b87)

diff --git a/builders/nginx.js b/builders/nginx.js
--- a/builders/nginx.js
+++ b/builders/nginx.js
@@ -26,6 +26,7 @@
       '1.17',
       '1.16',
     ],
+    backends: [],
     pinPairs: {
       '1': 'bitnamilegacy/nginx:1.29.1-debian-12-r0',
       '1.29': 'bitnamilegacy/nginx:1.29.1-debian-12-r0',
@@ -108,6 +109,11 @@
         ],
       };
 
+      // Add backend dependencies if specified
+      if (options.backends && options.backends.length > 0) {
+        nginx.depends_on = options.backends;
+      }
+
       // Send it downstream
       super(id, options, {services: _.set({}, options.name, nginx)});
     }