Nodejs fetch and Traefik

Traefik Traefik v2
1

Hi Guys, we have a docker compose with a traefik (v2.11) as a proxy for multiple services (postgres, keycloak, api, front, ...)

I have a problem because a traefik hostname is accessible from the browser (nice) but not from a nodejs application that use fetch. As far as i known it's probably a DNS issue, but i can't find a way to resolve it.

http:
  routers:
    traefik:
      rule: "Host(`traefik.docker.localhost`)"
      service: "api@internal"
      tls:
        domains:
          - main: "docker.localhost"
            sans:
              - "*.docker.localhost"

tls:
  certificates:
    - certFile: "/etc/traefik/ssl/local-cert.pem"
      keyFile: "/etc/traefik/ssl/local-key.pem"

global:
  sendAnonymousUsage: false

api:
  dashboard: true
  insecure: true

providers:
  docker:
    endpoint: "unix:///var/run/docker.sock"
    watch: true
    exposedByDefault: false

  file:
    filename: /etc/traefik/config.yml
    watch: true

log:
  level: INFO
  format: common

accessLog: {}

entryPoints:
  http:
    address: ":80"
    http:
      redirections:
        entryPoint:
          to: https
          scheme: https
  https:
    address: ":443"
  postgres:
    address: ":5432"

and the keycloak docker compose configuration

  keycloak:
    image: ${REGISTRY:-msdepi}/keycloak:${PLATFORM:-linux}-${TAG:-latest}
    profiles:
      - infra
    build: ./.local/.keycloak
    environment:
      KEYCLOAK_ADMIN: admin
      KEYCLOAK_ADMIN_PASSWORD: ${KEYCLOAK_ADMIN_PASSWORD}
      KC_DB: postgres
      KC_DB_URL_HOST: postgres
      KC_DB_USERNAME: postgres
      KC_DB_PASSWORD: ${POSTGRES_PASSWORD}
      KC_DB_URL_DATABASE: ${DB_NAME}
      KC_DB_SCHEMA: public
      KC_PROXY: edge
      KC_HTTP_ENABLE: true
      KC_HTTP_HOST: 0.0.0.0
      KC_HOSTNAME_STRICT: false
      KC_HOSTNAME: keycloak.docker.localhost
    command: start --import-realm
    volumes:
      - ./.local/.keycloak/realm-config/:/opt/keycloak/data/import/
    depends_on:
      postgres:
        condition: service_healthy
    labels:
      - "traefik.enable=true"
      - "traefik.http.services.keycloak.loadbalancer.server.port=8080"
      - "traefik.http.services.keycloak.entrypoints=http"
      - "traefik.http.routers.keycloak.rule=Host(`keycloak.docker.localhost`)"
      - "traefik.http.routers.keycloak.tls=true"
2

Whe using the fetch in node

fetch('https://keycloak.docker.localhost/')
  .then(resp => console.log(resp))
  .catch(err => console.error(err))

i have this error

TypeError: fetch failed
    at Object.fetch (node:internal/deps/undici/undici:11457:11)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  cause: Error: getaddrinfo ENOTFOUND keycloak.docker.localhost
      at GetAddrInfoReqWrap.onlookup [as oncomplete] (node:dns:107:26) {
    errno: -3008,
    code: 'ENOTFOUND',
    syscall: 'getaddrinfo',
    hostname: 'keycloak.docker.localhost'
  }
}

which just says that it can't resolve the domain name

3

Did you configure those domains in your local hosts file or on your DSL router?

4

No, but the keycloak.docker.localhost is acessible from the browser without any issue but not from node. Which i need to authenticate my user from the NextJs application

5

Some browsers are automatically resolving any *.localhost to 127.0.0.1. Node will not do that.

6

ok thanks.
So if i have everything inside docker, will node be able to resolve the domain name through the docker dns ?

7

Not with localhost, but with service/container names.