Adding CORS support to nginx proxy in Kubernetes
At work, for a couple of months now, we’ve been using Ambassador as our main API gateway to our k8s services. We also have our own authorization service that uses Ambassador’s AuthService mechanism. Recently, we’ve had services that needed CORS support and although Ambassador has features that support the enabling of CORS, we had to update our authorization service to handle CORS-related requests. Instead of doing this, we tried adding the CORS support at the proxy level (nginx). I’ve wrote about this topic here and here.
In the example below, the CORS support is added under the location /svc2/.
---
apiVersion: v1
kind: ConfigMap
metadata:
name: serviceproxy-conf
data:
serviceproxy.conf: |
server {
listen 80;
server_name development.mobingi.com;
resolver kube-dns.kube-system.svc.cluster.local valid=10s;
location ~ ^/svc1/(.*)$ {
auth_basic "mobingi";
auth_basic_user_file /etc/serviceproxy/htpasswd;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header Host $host;
rewrite ^/svc1/(.*)$ /$1 break;
proxy_pass "http://svc1.default.svc.cluster.local";
proxy_http_version 1.1;
}
location ~ ^/svc2/(.*)$ {
# Ref: https://enable-cors.org/server_nginx.html
if ($request_method = 'OPTIONS') {
add_header 'Access-Control-Allow-Origin' '*';
add_header 'Access-Control-Allow-Methods' 'POST, OPTIONS';
# Custom headers and headers various browsers *should* be OK with but aren't.
add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization';
# Tell client that this pre-flight info is valid for 20 days.
add_header 'Access-Control-Max-Age' 1728000;
add_header 'Content-Type' 'text/plain; charset=utf-8';
add_header 'Content-Length' 0;
return 204;
}
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header Host $host;
rewrite ^/svc2/(.*)$ /$1 break;
proxy_pass "http://svc2.default.svc.cluster.local";
proxy_http_version 1.1;
}
# root health check requirement in GKE ingress
location / {
return 200 'healthy\n';
}
}
{..redacted..}With that said, be aware of the potential problems of using if in nginx.
---If you have any questions or feedback, please reach out @flowerinthenyt.
