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[GH-ISSUE #4572] Unable to proxy requests using the container’s DNS name: 502 Bad Gateway #2920

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opened 2026-02-26 07:37:12 +03:00 by kerem · 1 comment

kerem commented

2026-02-26 07:37:12 +03:00

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Originally created by @gremo on GitHub (Jun 9, 2025).
Original GitHub issue: https://github.com/NginxProxyManager/nginx-proxy-manager/issues/4572

Checklist

Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
- Yes
Are you sure you're not using someone else's docker image?
- Yes
Have you searched for similar issues (both open and closed)?
- Yes

Describe the bug

I'm spending hours and days trying to figure out what's wrong with this setup. Based on my understanding of Docker, when creating an internal network, containers should be able to communicate using DNS names. And in fact, they do — from inside Nginx Proxy Manager I can reach the other container. But the proxy host keeps giving me a bad gateway. Proxy works only when using the container's IP address.

Tested with different containers: homeassistant, portainer, filebrowser, healthchecks. All works fine with Ip address.

Create the internal network: docker network create internal --internal
Spin a NPM container with the default bridge network
Add the internal network: docker network connect internal nginx-proxy-manager
Run a simple container like filebrowser with the internal network only (do not expose port, isolate it)
Create a proxy host to filebrowser:80, that is using container DNS

Container filebrowser networking (relevant part):

"NetworkSettings": {
    "Bridge": "",
    "Networks": {
        "internal": {
            "IPAddress": "172.19.0.4",
            "DNSNames": [
                "filebrowser",
                "d2099f13c0b0"
            ]
        }
    }
}

Container nginx-proxy-manager networking (relevant part):

"Networks": {
    "external": {
        "Gateway": "172.20.0.1",
        "IPAddress": "172.20.0.2",
        "DNSNames": [
            "nginx-proxy-manager",
            "603c8bc176a1"
        ]
    },
    "internal": {
        "IPAddress": "172.19.0.3",
        "DNSNames": [
            "nginx-proxy-manager",
            "603c8bc176a1"
        ]
    }
}

From inside the container curl -v http://filebrowser show the HTML page.

Nginx Proxy Manager Version
v2.12.3

Expected behavior
Should proxy requests using container’s DNS name.

Operating System
RaspberryPi 4B running Raspberry os-lite

Originally created by @gremo on GitHub (Jun 9, 2025). Original GitHub issue: https://github.com/NginxProxyManager/nginx-proxy-manager/issues/4572  **Checklist** - Have you pulled and found the error with `jc21/nginx-proxy-manager:latest` docker image? - Yes - Are you sure you're not using someone else's docker image? - Yes - Have you searched for similar issues (both open and closed)? - Yes **Describe the bug** I'm spending hours and days trying to figure out what's wrong with this setup. Based on my understanding of Docker, when creating an internal network, **containers should be able to communicate using DNS names**. And in fact, they do — from inside Nginx Proxy Manager I can reach the other container. But the proxy host keeps giving me a bad gateway. Proxy works only when using the container's IP address. Tested with different containers: homeassistant, portainer, filebrowser, healthchecks. All works fine with Ip address. 1. Create the internal network: `docker network create internal --internal` 2. Spin a NPM container with the default bridge network 3. Add the internal network: `docker network connect internal nginx-proxy-manager` 4. Run a simple container like filebrowser with the `internal` network only (do not expose port, isolate it) 5. Create a proxy host to `filebrowser:80`, that is using container DNS ![Image](https://github.com/user-attachments/assets/5043fabc-705c-4699-935c-694766fc1999) **Container filebrowser** networking (relevant part): ```json "NetworkSettings": { "Bridge": "", "Networks": { "internal": { "IPAddress": "172.19.0.4", "DNSNames": [ "filebrowser", "d2099f13c0b0" ] } } } ``` **Container nginx-proxy-manager** networking (relevant part): ```json "Networks": { "external": { "Gateway": "172.20.0.1", "IPAddress": "172.20.0.2", "DNSNames": [ "nginx-proxy-manager", "603c8bc176a1" ] }, "internal": { "IPAddress": "172.19.0.3", "DNSNames": [ "nginx-proxy-manager", "603c8bc176a1" ] } } ``` From inside the container `curl -v http://filebrowser` show the HTML page. **Nginx Proxy Manager Version** v2.12.3 **Expected behavior** Should proxy requests using container’s DNS name. **Operating System** RaspberryPi 4B running Raspberry os-lite

kerem

2026-02-26 07:37:12 +03:00

closed this issue
added the
bug
label

kerem commented

2026-02-26 07:37:13 +03:00

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@gremo commented on GitHub (Jun 19, 2025):

Recreating everything from scratch solved the issue. Maybe something got corrupted — I’m not sure. For anyone facing the same problem: unfortunately, try deleting the data and reconfiguring your proxy hosts.

@gremo commented on GitHub (Jun 19, 2025): Recreating everything from scratch solved the issue. Maybe something got corrupted — I’m not sure. For anyone facing the same problem: unfortunately, try deleting the data and reconfiguring your proxy hosts.

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starred/nginx-proxy-manager-NginxProxyManager#2920

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