NGINX can't resolve upstream name from it's own config

Question

I have a MarkLogic cluster set up in docker and I wanted to add nginx as a load balancer so I can access all hosts on the same ports. The basic configuration doesn't work, when I try to access http://localhost:8001 for example, nginx logs an error

172.19.0.1 - - [09/Sep/2025:08:30:17 +0000] "GET / HTTP/1.1" 502 559 "http://localhost:8001/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36" 2025/09/09 08:30:17 [error] 62#62: *6 no resolver defined to resolve cluster_m, client: 172.19.0.1, server: , request: "GET / HTTP/1.1", host: "localhost:8001", referrer: "http://localhost:8001/" 

What am I missing here? Attached the nginx.conf and a docker-compose.yaml. Any help greately appreciated.

nginx version: nginx/1.29.1

events {} http { upstream cluster_m { resolver 127.0.0.11; server bootstrap_3n; server node2; server node3; } server { listen 7997-8074; location / { proxy_set_header Host $host; proxy_pass http://cluster_m:$server_port; } } } 

name: marklogic-cluster services: nginx: image: nginx container_name: nginx volumes: - ./nginx.conf:/etc/nginx/nginx.conf:ro ports: - 7197:7997 - 8000-8010:8000-8010 - 8020-8074:8020-8074 depends_on: - bootstrap_3n networks: - external_net bootstrap_3n: image: progressofficial/marklogic-db:latest-11 container_name: bootstrap_3n hostname: bootstrap_3n dns_search: "" environment: - MARKLOGIC_INIT=true - MARKLOGIC_ADMIN_USERNAME_FILE=mldb_admin_username - MARKLOGIC_ADMIN_PASSWORD_FILE=mldb_admin_password - TZ=Europe/Prague volumes: - MarkLogic_3n_vol1:/var/opt/MarkLogic secrets: - mldb_admin_password - mldb_admin_username networks: - external_net node2: image: progressofficial/marklogic-db:latest-11 container_name: node2 hostname: node2 dns_search: "" environment: - MARKLOGIC_INIT=true - MARKLOGIC_ADMIN_USERNAME_FILE=mldb_admin_username - MARKLOGIC_ADMIN_PASSWORD_FILE=mldb_admin_password - MARKLOGIC_JOIN_CLUSTER=true - MARKLOGIC_BOOTSTRAP_HOST=bootstrap_3n - TZ=Europe/Prague volumes: - MarkLogic_3n_vol2:/var/opt/MarkLogic secrets: - mldb_admin_password - mldb_admin_username depends_on: - bootstrap_3n networks: - external_net node3: image: progressofficial/marklogic-db:latest-11 container_name: node3 hostname: node3 dns_search: "" environment: - MARKLOGIC_INIT=true - MARKLOGIC_ADMIN_USERNAME_FILE=mldb_admin_username - MARKLOGIC_ADMIN_PASSWORD_FILE=mldb_admin_password - MARKLOGIC_JOIN_CLUSTER=true - MARKLOGIC_BOOTSTRAP_HOST=bootstrap_3n - TZ=Europe/Prague volumes: - MarkLogic_3n_vol3:/var/opt/MarkLogic secrets: - mldb_admin_password - mldb_admin_username depends_on: - bootstrap_3n networks: - external_net secrets: mldb_admin_password: file: ./mldb_admin_password.txt mldb_admin_username: file: ./mldb_admin_username.txt networks: external_net: {} volumes: MarkLogic_3n_vol1: MarkLogic_3n_vol2: MarkLogic_3n_vol3: 

I tried adding the resolver in server and location blocks set to 127.0.0.1 and 127.0.0.11 but it didn't work.

Answer 1

Looks like it's not possible to do it the way I wanted. So I came up with a solution. I defined an upstream for each port and luckily the $server_port variable can be used in the proxy_pass instruction like that proxy_pass http://cluster_$server_port;. With envsubst I generated the upstream configs for each port from a range and then included them with include nginx-config/config_*.conf; in the nginx.conf.

Final compose and config files look like that:

 nginx: image: nginx container_name: nginx volumes: - ./nginx.conf:/etc/nginx/nginx.conf:ro - ./nginx-config:/etc/nginx/nginx-config:ro ports: - 8000-8074:8000-8074 depends_on: - bootstrap_3n networks: - external_net 

events { worker_connections 1024; } http { proxy_set_header Host $http_host; proxy_redirect off; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header X-Forwarded-Proto $scheme; proxy_set_header X-NginX-Proxy true; include nginx-config/config_*.conf; server { listen 8000-8074; location / { proxy_pass http://cluster_$server_port; } } } 

The template I used and shell script to generate upstream configs:

 upstream cluster_${INT} { resolver 127.0.0.11; server bootstrap_3n:${INT}; server node2:${INT}; server node3:${INT}; } 

script

#!/bin/bash for INT in {8000..8074}; do export INT envsubst < "int.conf.template" > "config_$INT.conf" done