Add 503 status code when there are zero upstream endpoints #3406

bjee19 · 2025-05-27T22:23:51Z

Proposed changes

Add 503 status code when there are zero upstream endpoints.

Problem: When using NGINX Plus, the generated state file for an upstream was not correctly generating the 503 server for upstreams with zero endpoints.

Solution: On upstreams with zero endpoints, generate the correct nginx conf in the state file.

Testing: The 503 server socket shows up in the nginx plus API dashboard, both when initially deploying resources, and when scaling the deployment as described in #2090. Sending traffic to the upstream with zero endpoints correctly returns a 503 status code (instead of 502 as previously) and there is no longer an error message outputted in the nginx logs. Verified after deployment/pod gets ready, so the upstream endpoint becomes valid, the state file is updated correctly to have the correct upstream endpoint, and traffic flows correctly.

Closes #2090

Checklist

Before creating a PR, run through this checklist and mark each as complete.

I have read the CONTRIBUTING doc
I have added tests that prove my fix is effective or that my feature works
I have checked that all unit tests pass after adding my changes
I have updated necessary documentation
I have rebased my branch onto main
I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

internal/mode/static/nginx/agent/agent.go

bjee19 · 2025-05-27T22:26:06Z

nginx conf here:

~/Code/nginx-gateway-fabric/examples/cafe-example main ⇡1281 *6 !2 ❯ kubectl exec -it gateway-nginx-9d9bbc669-spv6b -- nginx -T                                                                     ⎈ kind-kind
Defaulted container "nginx" out of: nginx, init (init)
2025/05/27 22:06:31 [notice] 131#131: js vm init njs: 0000FFFF8D566A00
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
# configuration file /etc/nginx/nginx.conf:
load_module /usr/lib/nginx/modules/ngx_http_js_module.so;
include /etc/nginx/main-includes/*.conf;

worker_processes auto;

pid /var/run/nginx/nginx.pid;

events {
  worker_connections 1024;
}

http {
  include /etc/nginx/conf.d/*.conf;
  include /etc/nginx/mime.types;
  js_import /usr/lib/nginx/modules/njs/httpmatches.js;

  default_type application/octet-stream;

  proxy_headers_hash_bucket_size 512;
  proxy_headers_hash_max_size 1024;
  server_names_hash_bucket_size 256;
  server_names_hash_max_size 1024;
  variables_hash_bucket_size 512;
  variables_hash_max_size 1024;

  sendfile on;
  tcp_nopush on;

  server_tokens off;
}

stream {
  variables_hash_bucket_size 512;
  variables_hash_max_size 1024;

  map_hash_max_size 2048;
  map_hash_bucket_size 256;

  log_format stream-main '$remote_addr [$time_local] '
                         '$protocol $status $bytes_sent $bytes_received '
                         '$session_time "$ssl_preread_server_name"';
  access_log /dev/stdout stream-main;
  include /etc/nginx/stream-conf.d/*.conf;
}

# configuration file /etc/nginx/main-includes/main.conf:

error_log stderr info;


# configuration file /etc/nginx/main-includes/mgmt.conf:

mgmt {
        license_token /etc/nginx/secrets/license.jwt;
        deployment_context /etc/nginx/main-includes/deployment_ctx.json;
}

# configuration file /etc/nginx/conf.d/http.conf:
http2 on;

# Set $gw_api_compliant_host variable to the value of $http_host unless $http_host is empty, then set it to the value
# of $host. We prefer $http_host because it contains the original value of the host header, which is required by the
# Gateway API. However, in an HTTP/1.0 request, it's possible that $http_host can be empty. In this case, we will use
# the value of $host. See http://nginx.org/en/docs/http/ngx_http_core_module.html#var_host.
map $http_host $gw_api_compliant_host {
    '' $host;
    default $http_host;
}

# Set $connection_header variable to upgrade when the $http_upgrade header is set, otherwise, set it to close. This
# allows support for websocket connections. See https://nginx.org/en/docs/http/websocket.html.
map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;
}

## Returns just the path from the original request URI.
map $request_uri $request_uri_path {
  "~^(?P<path>[^?]*)(\?.*)?$"  $path;
}


js_preload_object matches from /etc/nginx/conf.d/matches.json;
server {
    listen 80 default_server;
    listen [::]:80 default_server;
    default_type text/html;
    return 404;
}

server {
    listen 80;
    listen [::]:80;

    server_name cafe.example.com;
    status_zone cafe.example.com;

        
    location /coffee/ {
        

        

        proxy_http_version 1.1;
        proxy_set_header Host "$gw_api_compliant_host";
        proxy_set_header X-Forwarded-For "$proxy_add_x_forwarded_for";
        proxy_set_header X-Real-IP "$remote_addr";
        proxy_set_header X-Forwarded-Proto "$scheme";
        proxy_set_header X-Forwarded-Host "$host";
        proxy_set_header X-Forwarded-Port "$server_port";
        proxy_set_header Upgrade "$http_upgrade";
        proxy_set_header Connection "$connection_upgrade";
        proxy_pass http://default_coffee_80$request_uri;
            
            
            
    }
    location = /coffee {
        

        

        proxy_http_version 1.1;
        proxy_set_header Host "$gw_api_compliant_host";
        proxy_set_header X-Forwarded-For "$proxy_add_x_forwarded_for";
        proxy_set_header X-Real-IP "$remote_addr";
        proxy_set_header X-Forwarded-Proto "$scheme";
        proxy_set_header X-Forwarded-Host "$host";
        proxy_set_header X-Forwarded-Port "$server_port";
        proxy_set_header Upgrade "$http_upgrade";
        proxy_set_header Connection "$connection_upgrade";
        proxy_pass http://default_coffee_80$request_uri;
            
            
            
    }
    location = /tea {
        

        

        proxy_http_version 1.1;
        proxy_set_header Host "$gw_api_compliant_host";
        proxy_set_header X-Forwarded-For "$proxy_add_x_forwarded_for";
        proxy_set_header X-Real-IP "$remote_addr";
        proxy_set_header X-Forwarded-Proto "$scheme";
        proxy_set_header X-Forwarded-Host "$host";
        proxy_set_header X-Forwarded-Port "$server_port";
        proxy_set_header Upgrade "$http_upgrade";
        proxy_set_header Connection "$connection_upgrade";
        proxy_pass http://default_tea_80$request_uri;
            
            
            
    }
    location / {
        
        return 404 "";

        

        proxy_http_version 1.1;
    }
}

server {
    listen unix:/var/run/nginx/nginx-503-server.sock;
    access_log off;

    return 503;
}

server {
    listen unix:/var/run/nginx/nginx-500-server.sock;
    access_log off;

    return 500;
}


upstream default_coffee_80 {
    random two least_conn;
    zone default_coffee_80 1m;
    
    state /var/lib/nginx/state/default_coffee_80.conf;
    
    
    
    
}

upstream default_tea_80 {
    random two least_conn;
    zone default_tea_80 1m;
    
    state /var/lib/nginx/state/default_tea_80.conf;
    
    
    
    
}

upstream invalid-backend-ref {
    random two least_conn;
    
        
    server unix:/var/run/nginx/nginx-500-server.sock;
    
    
    
    
}





# configuration file /var/lib/nginx/state/default_coffee_80.conf:
server 10.244.0.7:8080;

# configuration file /var/lib/nginx/state/default_tea_80.conf:
server unix:/var/run/nginx/nginx-503-server.sock;

# configuration file /etc/nginx/conf.d/plus-api.conf:

server {
    listen unix:/var/run/nginx/nginx-plus-api.sock;
    access_log off;

    location /api {
      api write=on;
    }
}

server {
    listen 8765;
    root /usr/share/nginx/html;
    access_log off;
    
    allow 127.0.0.1;
    deny all;

    location = /dashboard.html {}

    location /api {
      api write=off;
    }
}

# configuration file /etc/nginx/mime.types:

types {
    text/html                                        html htm shtml;
    text/css                                         css;
    text/xml                                         xml;
    image/gif                                        gif;
    image/jpeg                                       jpeg jpg;
    application/javascript                           js;
    application/atom+xml                             atom;
    application/rss+xml                              rss;

    text/mathml                                      mml;
    text/plain                                       txt;
    text/vnd.sun.j2me.app-descriptor                 jad;
    text/vnd.wap.wml                                 wml;
    text/x-component                                 htc;

    image/avif                                       avif;
    image/png                                        png;
    image/svg+xml                                    svg svgz;
    image/tiff                                       tif tiff;
    image/vnd.wap.wbmp                               wbmp;
    image/webp                                       webp;
    image/x-icon                                     ico;
    image/x-jng                                      jng;
    image/x-ms-bmp                                   bmp;

    font/woff                                        woff;
    font/woff2                                       woff2;

    application/java-archive                         jar war ear;
    application/json                                 json;
    application/mac-binhex40                         hqx;
    application/msword                               doc;
    application/pdf                                  pdf;
    application/postscript                           ps eps ai;
    application/rtf                                  rtf;
    application/vnd.apple.mpegurl                    m3u8;
    application/vnd.google-earth.kml+xml             kml;
    application/vnd.google-earth.kmz                 kmz;
    application/vnd.ms-excel                         xls;
    application/vnd.ms-fontobject                    eot;
    application/vnd.ms-powerpoint                    ppt;
    application/vnd.oasis.opendocument.graphics      odg;
    application/vnd.oasis.opendocument.presentation  odp;
    application/vnd.oasis.opendocument.spreadsheet   ods;
    application/vnd.oasis.opendocument.text          odt;
    application/vnd.openxmlformats-officedocument.presentationml.presentation
                                                     pptx;
    application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
                                                     xlsx;
    application/vnd.openxmlformats-officedocument.wordprocessingml.document
                                                     docx;
    application/vnd.wap.wmlc                         wmlc;
    application/wasm                                 wasm;
    application/x-7z-compressed                      7z;
    application/x-cocoa                              cco;
    application/x-java-archive-diff                  jardiff;
    application/x-java-jnlp-file                     jnlp;
    application/x-makeself                           run;
    application/x-perl                               pl pm;
    application/x-pilot                              prc pdb;
    application/x-rar-compressed                     rar;
    application/x-redhat-package-manager             rpm;
    application/x-sea                                sea;
    application/x-shockwave-flash                    swf;
    application/x-stuffit                            sit;
    application/x-tcl                                tcl tk;
    application/x-x509-ca-cert                       der pem crt;
    application/x-xpinstall                          xpi;
    application/xhtml+xml                            xhtml;
    application/xspf+xml                             xspf;
    application/zip                                  zip;

    application/octet-stream                         bin exe dll;
    application/octet-stream                         deb;
    application/octet-stream                         dmg;
    application/octet-stream                         iso img;
    application/octet-stream                         msi msp msm;

    audio/midi                                       mid midi kar;
    audio/mpeg                                       mp3;
    audio/ogg                                        ogg;
    audio/x-m4a                                      m4a;
    audio/x-realaudio                                ra;

    video/3gpp                                       3gpp 3gp;
    video/mp2t                                       ts;
    video/mp4                                        mp4;
    video/mpeg                                       mpeg mpg;
    video/quicktime                                  mov;
    video/webm                                       webm;
    video/x-flv                                      flv;
    video/x-m4v                                      m4v;
    video/x-mng                                      mng;
    video/x-ms-asf                                   asx asf;
    video/x-ms-wmv                                   wmv;
    video/x-msvideo                                  avi;
}

# configuration file /etc/nginx/stream-conf.d/stream.conf:


server {
    listen unix:/var/run/nginx/connection-closed-server.sock;
    return "";
}

Showing the correct state file. This is the same for both initial deployment of resources and when scaling the tea deployment.

codecov · 2025-05-27T22:26:26Z

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.77%. Comparing base (209f028) to head (f29f0b4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3406      +/-   ##
==========================================
- Coverage   86.82%   86.77%   -0.06%     
==========================================
  Files         127      127              
  Lines       15011    15020       +9     
  Branches       62       62              
==========================================
  Hits        13034    13034              
- Misses       1828     1835       +7     
- Partials      149      151       +2

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bjee19 · 2025-05-27T22:27:05Z

Here's some traffic results showing the correct 503 status code:

~/Code/nginx-gateway-fabric/examples/cafe-example main ⇡1281 *6 !2 ❯ curl --resolve cafe.example.com:8080:127.0.0.1 http://cafe.example.com:8080/tea --insecure 
<html>
<head><title>503 Service Temporarily Unavailable</title></head>
<body>
<center><h1>503 Service Temporarily Unavailable</h1></center>
<hr><center>nginx</center>
</body>
</html>

Here is a snippet of the nginx logs showing no errors when returning a 503:

2025/05/27 22:05:55 [info] 66#66: *73 client closed connection while waiting for request, client: unix:, server: unix:/var/run/nginx/nginx-plus-api.sock
2025/05/27 22:05:55 [info] 72#72: *25 client unix: closed keepalive connection
2025/05/27 22:05:55 [info] 66#66: *70 client unix: closed keepalive connection
2025/05/27 22:05:55 [info] 66#66: *33 client unix: closed keepalive connection
127.0.0.1 - - [27/May/2025:22:05:56 +0000] "GET /tea HTTP/1.1" 503 190 "-" "curl/8.7.1"
2025/05/27 22:05:56 [info] 66#66: *64 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:56 [info] 66#66: *67 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:56 [info] 66#66: *66 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:56 [info] 66#66: *65 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:56 [info] 66#66: *63 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:56 [info] 66#66: *62 client 127.0.0.1 closed keepalive connection
127.0.0.1 - - [27/May/2025:22:05:56 +0000] "GET /tea HTTP/1.1" 503 190 "-" "curl/8.7.1"
2025/05/27 22:05:57 [info] 67#67: *76 client 127.0.0.1 closed keepalive connection
127.0.0.1 - - [27/May/2025:22:05:57 +0000] "GET /tea HTTP/1.1" 503 190 "-" "curl/8.7.1"
2025/05/27 22:05:57 [info] 68#68: *85 client 127.0.0.1 closed keepalive connection
2025/05/27 22:05:58 [info] 69#69: *88 client 127.0.0.1 closed keepalive connection
2025/05/27 22:06:01 [info] 66#66: *80 client 127.0.0.1 closed keepalive connection
2025/05/27 22:06:01 [info] 67#67: *83 client 127.0.0.1 closed keepalive connection

bjee19 · 2025-05-27T22:30:19Z

This is what the dashboard looks like, both after deploying the resources initially and when scaling the tea deployment. I couldn't screenshot it showing the full name, but the name of the server in the tea upstream is the 503 socket.

salonichf5 · 2025-05-27T22:53:51Z

This is what the dashboard looks like, both after deploying the resources initially and when scaling the tea deployment. I couldn't screenshot it showing the full name, but the name of the server in the tea upstream is the 503 socket.

Looks great 🚀

bjee19 requested a review from a team as a code owner May 27, 2025 22:23

github-project-automation bot added this to NGINX Gateway Fabric May 27, 2025

github-project-automation bot moved this to 🆕 New in NGINX Gateway Fabric May 27, 2025

github-actions bot added the bug Something isn't working label May 27, 2025

sjberman reviewed May 27, 2025

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internal/mode/static/nginx/agent/agent.go Outdated Show resolved Hide resolved

Add 503 status code when there are zero upstream endpoints

94598cf

bjee19 force-pushed the bug/fix-nginx-plus-state-file-generation branch from 3cbe049 to 94598cf Compare May 27, 2025 22:28

bjee19 added 3 commits May 27, 2025 15:47

Add shared types file for exported 503 constant

46fdb71

Change to types package

a9a6f2d

Remove expected error message

f29f0b4

github-actions bot added the tests Pull requests that update tests label May 27, 2025

salonichf5 approved these changes May 27, 2025

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sjberman approved these changes May 27, 2025

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bjee19 merged commit 44472e9 into main May 27, 2025
62 of 63 checks passed

bjee19 deleted the bug/fix-nginx-plus-state-file-generation branch May 27, 2025 23:33

github-project-automation bot moved this from 🆕 New to ✅ Done in NGINX Gateway Fabric May 27, 2025

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