Getting API error 502 for /music/api/default in the webapp

[einarpersson]

Hi, I'm a new user here. I have mympd/mpd running on a home server with docker and caddy reverse proxy. It works as intended but I'm getting a 502 notification now and then, which I'd like to understand and fix if possible.

API error
Error accessing /music/api/default
Response code: 502 - 

Here's my docker compose snippet

  mympd:
    image: ghcr.io/jcorporation/mympd/mympd
    container_name: mympd
    # ports:
    #   - 8080:8080
    user: 1000:1000
    environment:
      - UMASK_SET=022
      - MYMPD_SSL=false
      - MYMPD_HTTP_PORT=8080
    volumes:
      - /run/user/1000/mpd:/run/mpd
      - /home/einar/.local/state/mympd/workdir:/var/lib/mympd
      - /home/einar/.cache/mympd:/var/cache/mympd
      - /data/external/media/music:/var/lib/mpd/music:ro
      - /home/einar/.local/state/mpd/playlists:/var/lib/mpd/playlists:ro
    restart: unless-stopped
    networks:
       - infra

and by caddy file

mydomain.local {
  tls internal

        handle_path /music/* {
                        reverse_proxy http://mympd:8080 {
                                        header_up Host {host}
                                        header_up X-Real-IP {remote_host}
                                        header_up X-Forwarded-For {remote_host}
                                        header_up X-Forwarded-Proto {scheme}
                        }
        }
}

and my mpd conf

music_directory    "/data/external/media/music"
playlist_directory "/home/einar/.local/state/mpd/playlists"
db_file            "/home/einar/.cache/mpd/db"
state_file         "/home/einar/.local/state/mpd/state"

partition {
    name "foo"
}

audio_output {
    type            "pulse"
    name            "PulseAudio"
    mixer_type      "software"
}

As I said, this works but I'd like to get rid of that annoying 502 notification, and also understand if I have something wrong in my setup.

Grateful for any advice!

[jcorporation]

Setup looks good. HTTP code 502 is Bad Gateway. Request logs from caddy and debug logs from myMPD would be useful and also a HAR file from your browser.

I run myMPD in one of my setups behind a NGINX reverse proxy and it works without problems.

[stefanroellin]

@einarpersson: have found a solution for the 502 api error? I observe the same error with a similar setup as you have.

[einarpersson]

Unfortunately no

[jcorporation]

Provide the requested logs and I will investigate

[stefanroellin]

I will send you the logs by private email. Some observations:

• I first thought the problem happens only, if caddy and mympd run on a Raspberry Pi. However, I could reproduce the same error on an amd64 architecture.
• If the site is reloaded, it fails about three out of four times with an api error. In other words, it does not always fail.
• The failing request is not always the same.
• In the caddy logs the error "http: server closed idle connection" appears in case of an api error.

[jcorporation]

You can try disabling keep-alive on server side in caddy.

[stefanroellin]

Thanks for the suggestion! This has indeed solved the api error. I use the following Caddyfile and have not had a problem since:

music {
        reverse_proxy http://mympd:8080 {
                transport http {
                        keepalive off
                }
        }
}

[jcorporation]

After looking in your logs: Caddy does not set set a "Connection: keep-alive" header in it's requests. myMPD's default is closing the connection if it does not find the "Connection: keep-alive" header. Is seems that http/1.1 defaults to persistent connections and myMPD behaves incorrectly.

I open a bug. Fix is fairly simple, but must be tested thoroughly.