urllib3.exceptions.NameResolutionError ([Errno -2] Name does not resolve)

[igolman]

Hi 👋

firstly thank you and all supporters that have contributed to the last v1.5.3 release 👍

I've just picked up the latest image and encounter with a problem on my setup. I have to mention in advance, that instead of mounting the docker socket in stackback container directly, I use a "backupproxy" container based on the linuxproxy project. The configuration of a proxy is quite standard:

services:
  backupproxy:
    image: 'linuxserver/socket-proxy:3.2.7'
    container_name: 'backupproxy'
    environment:
      CONTAINERS: 1
      VERSION: 1
      POST: 1
      ALLOW_START: 1
      ALLOW_STOP: 1
    read_only: true
    tmpfs: [ '/run' ]
    volumes: [ '/var/run/docker.sock:/var/run/docker.sock:ro' ]
    restart: 'unless-stopped'
    networks: [ 'backup' ]

the stackback instance is configured with DOCKER_HOST variable instead of a socket mount:

services:
  stackback_s3:
    image: 'ghcr.io/lawndoc/stack-back:v1.5.3'
    volumes:
      - 'backup_s3_cache:/cache'
    restart: 'unless-stopped'
    environment:
      DOCKER_HOST: 'tcp://backupproxy:2375'
      RESTIC_REPOSITORY: "${RESTIC_S3_REPOSITORY:?}"
      RESTIC_PASSWORD: "${RESTIC_S3_PASSPHRASE:?}"
      AWS_ACCESS_KEY_ID: "${RESTIC_AWS_ACCESS_KEY_ID:?}"
      AWS_SECRET_ACCESS_KEY: "${RESTIC_AWS_SECRET_ACCESS_KEY:?}"
      ...
      ...
    networks:
      default:
      backup:

with the v1.4.5 everything was working, however after update to v1.5.3:

• rcb status is still working

/restic-compose-backup # rcb status --log-level debug
2025-11-10 18:31:47,579 - INFO: Status for compose project 'my-project'
2025-11-10 18:31:47,579 - INFO: Repository: 's3:my-project'
2025-11-10 18:31:47,579 - INFO: Backup currently running?: False
2025-11-10 18:31:47,579 - INFO: Include project name in backup path?: False
2025-11-10 18:31:47,579 - DEBUG: Exclude bind mounts from backups?: False
2025-11-10 18:31:47,579 - DEBUG: Include all compose projects?: False
2025-11-10 18:31:47,579 - DEBUG: Use cache for integrity check?: False
2025-11-10 18:31:47,579 - INFO: Checking docker availability
2025-11-10 18:31:47,641 - INFO: Contacting repository
2025-11-10 18:31:47,641 - DEBUG: cmd: restic -r s3:my-project cat config
2025-11-10 18:31:48,768 - DEBUG: ---------- stdout ----------
2025-11-10 18:31:48,768 - DEBUG: {
2025-11-10 18:31:48,768 - DEBUG:   "version": 2,
2025-11-10 18:31:48,768 - DEBUG:   "id": "30e3595c4d35f1de43178f3a40f175305ce3b542b769741f67532200b6eb3f03",
2025-11-10 18:31:48,768 - DEBUG:   "chunker_polynomial": "2d58bfea5c1187"
2025-11-10 18:31:48,768 - DEBUG: }
2025-11-10 18:31:48,768 - DEBUG: ----------------------------
2025-11-10 18:31:48,768 - DEBUG: returncode 0
...
...
2025-11-10 18:31:48,771 - INFO: -------------------------------------------------------------------
/restic-compose-backup # echo $?
0

• rcb backup does not:

/restic-compose-backup # rcb backup --log-level debug
2025-11-10 18:32:02,618 - DEBUG: Starting backup container with image ghcr.io/lawndoc/stack-back:v1.5.3
2025-11-10 18:32:02,619 - INFO: Starting backup container
2025-11-10 18:32:02,907 - INFO: Backup process container: magical_easley
Traceback (most recent call last):
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connection.py", line 198, in _new_conn
    sock = connection.create_connection(
        (self._dns_host, self.port),
    ...<2 lines>...
        socket_options=self.socket_options,
    )
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/util/connection.py", line 60, in create_connection
    for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
               ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.14.0-linux-x86_64-musl/lib/python3.14/socket.py", line 983, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
               ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
socket.gaierror: [Errno -2] Name does not resolve

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connectionpool.py", line 787, in urlopen
    response = self._make_request(
        conn,
    ...<10 lines>...
        **response_kw,
    )
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connectionpool.py", line 493, in _make_request
    conn.request(
    ~~~~~~~~~~~~^
        method,
        ^^^^^^^
    ...<6 lines>...
        enforce_content_length=enforce_content_length,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connection.py", line 445, in request
    self.endheaders()
    ~~~~~~~~~~~~~~~^^
  File "/root/.local/share/uv/python/cpython-3.14.0-linux-x86_64-musl/lib/python3.14/http/client.py", line 1333, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.14.0-linux-x86_64-musl/lib/python3.14/http/client.py", line 1093, in _send_output
    self.send(msg)
    ~~~~~~~~~^^^^^
  File "/root/.local/share/uv/python/cpython-3.14.0-linux-x86_64-musl/lib/python3.14/http/client.py", line 1037, in send
    self.connect()
    ~~~~~~~~~~~~^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connection.py", line 276, in connect
    self.sock = self._new_conn()
                ~~~~~~~~~~~~~~^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connection.py", line 205, in _new_conn
    raise NameResolutionError(self.host, self, e) from e
urllib3.exceptions.NameResolutionError: <urllib3.connection.HTTPConnection object at 0x799ab4625550>: Failed to resolve 'backupproxy' ([Errno -2] Name does not resolve)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/requests/adapters.py", line 667, in send
    resp = conn.urlopen(
        method=request.method,
    ...<9 lines>...
        chunked=chunked,
    )
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/connectionpool.py", line 841, in urlopen
    retries = retries.increment(
        method, url, error=new_e, _pool=self, _stacktrace=sys.exc_info()[2]
    )
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/urllib3/util/retry.py", line 519, in increment
    raise MaxRetryError(_pool, url, reason) from reason  # type: ignore[arg-type]
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='backupproxy', port=2375): Max retries exceeded with url: /version (Caused by NameResolutionError("<urllib3.connection.HTTPConnection object at 0x799ab4625550>: Failed to resolve 'backupproxy' ([Errno -2] Name does not resolve)"))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/api/client.py", line 223, in _retrieve_server_version
    return self.version(api_version=False)["ApiVersion"]
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/api/daemon.py", line 181, in version
    return self._result(self._get(url), json=True)
                        ~~~~~~~~~^^^^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/utils/decorators.py", line 44, in inner
    return f(self, *args, **kwargs)
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/api/client.py", line 246, in _get
    return self.get(url, **self._set_request_timeout(kwargs))
           ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/requests/sessions.py", line 602, in get
    return self.request("GET", url, **kwargs)
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/requests/adapters.py", line 700, in send
    raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='backupproxy', port=2375): Max retries exceeded with url: /version (Caused by NameResolutionError("<urllib3.connection.HTTPConnection object at 0x799ab4625550>: Failed to resolve 'backupproxy' ([Errno -2] Name does not resolve)"))

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/restic-compose-backup/.venv/bin/rcb", line 10, in <module>
    sys.exit(main())
             ~~~~^^
  File "/restic-compose-backup/restic_compose_backup/cli.py", line 23, in main
    containers = RunningContainers()
  File "/restic-compose-backup/restic_compose_backup/containers.py", line 400, in __init__
    all_containers = utils.list_containers()
  File "/restic-compose-backup/restic_compose_backup/utils.py", line 39, in list_containers
    client = docker_client()
  File "/restic-compose-backup/restic_compose_backup/utils.py", line 29, in docker_client
    return docker.from_env()
           ~~~~~~~~~~~~~~~^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/client.py", line 94, in from_env
    return cls(
        timeout=timeout,
    ...<3 lines>...
        **kwargs_from_env(**kwargs)
    )
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/client.py", line 45, in __init__
    self.api = APIClient(*args, **kwargs)
               ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/api/client.py", line 207, in __init__
    self._version = self._retrieve_server_version()
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/restic-compose-backup/.venv/lib/python3.14/site-packages/docker/api/client.py", line 230, in _retrieve_server_version
    raise DockerException(
        f'Error while fetching server API version: {e}'
    ) from e
docker.errors.DockerException: Error while fetching server API version: HTTPConnectionPool(host='backupproxy', port=2375): Max retries exceeded with url: /version (Caused by NameResolutionError("<urllib3.connection.HTTPConnection object at 0x799ab4625550>: Failed to resolve 'backupproxy' ([Errno -2] Name does not resolve)"))
2025-11-10 18:32:03,774 - DEBUG: Container ExitCode 1
2025-11-10 18:32:03,800 - INFO: Backup container exit code: 1

• additional information:
  • both backupproxy and stackback instances are in backup docker network

/restic-compose-backup # ping backupproxy
PING backupproxy (10.11.0.2): 56 data bytes
64 bytes from 10.11.0.2: seq=0 ttl=64 time=0.062 ms
64 bytes from 10.11.0.2: seq=1 ttl=64 time=0.156 ms
^C
--- backupproxy ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.062/0.109/0.156 ms

• switching to direct docker socket mount in stackback solves the problem, i.e. with

services:
  stackback_s3:
    image: 'ghcr.io/lawndoc/stack-back:v1.5.3'
    volumes:
      - '/var/run/docker.sock:/tmp/docker.sock:ro'
      - 'backup_s3_cache:/cache'
    restart: 'unless-stopped'
    environment:
      # DOCKER_HOST: 'tcp://backupproxy:2375'

RFC. Any chance we can sort it out?

[lawndoc]

I think I know what happened. I was having issues while switching the database backups to the docker_exec method and added some manual DOCKER_HOST overrides to troubleshoot. I probably missed part of that cleanup. I'll try to make some time to resolve this soon.

[lawndoc]

Also just wanted to say I appreciate the detail in your issues, it makes it a lot easier to narrow down what might be happening.

[lawndoc]

Actually I did clean up all of the DOCKER_HOST overrides that I made during troubleshooting. It looks like the issue might actually be with your socket-proxy permissions.

I think you need to add EXEC: 1 to your socket-proxy environment due to the change in #72 which uses docker exec to back up databases rather than database clients over the docker network. I'll go test to confirm.

[lawndoc]

Ah okay, so 2 separate issues.

1. I removed too much of the network code in Backup databases through stdin via docker exec #72 and the backup runner no longer had access to the original stack-back container's network. This is the error you are seeing. I am fixing this in Add integration tests #75.
2. You will need to add EXEC: 1 to your socket-proxy environment as I described above.

I'll close this issue once #75 is merged.

[igolman]

Top! 👍 Grazie mille!