docker-compose/compose/service.py

from __future__ import absolute_import
from __future__ import unicode_literals

import logging
import os
import re
import sys
from collections import namedtuple
from operator import attrgetter

import enum
import six
from docker.errors import APIError
from docker.utils import LogConfig
from docker.utils.ports import build_port_bindings
from docker.utils.ports import split_port

from . import __version__
from .config import DOCKER_CONFIG_KEYS
from .config import merge_environment
from .config.validation import VALID_NAME_CHARS
from .const import DEFAULT_TIMEOUT
from .const import IS_WINDOWS_PLATFORM
from .const import LABEL_CONFIG_HASH
from .const import LABEL_CONTAINER_NUMBER
from .const import LABEL_ONE_OFF
from .const import LABEL_PROJECT
from .const import LABEL_SERVICE
from .const import LABEL_VERSION
from .container import Container
from .legacy import check_for_legacy_containers
from .progress_stream import stream_output
from .progress_stream import StreamOutputError
from .utils import json_hash
from .utils import parallel_execute

log = logging.getLogger(__name__)


DOCKER_START_KEYS = [
    'cap_add',
    'cap_drop',
    'devices',
    'dns',
    'dns_search',
    'env_file',
    'extra_hosts',
    'ipc',
    'read_only',
    'net',
    'log_driver',
    'log_opt',
    'mem_limit',
    'memswap_limit',
    'pid',
    'privileged',
    'restart',
    'volumes_from',
    'security_opt',
]


class BuildError(Exception):
    def __init__(self, service, reason):
        self.service = service
        self.reason = reason


class ConfigError(ValueError):
    pass


class NeedsBuildError(Exception):
    def __init__(self, service):
        self.service = service


class NoSuchImageError(Exception):
    pass


VolumeSpec = namedtuple('VolumeSpec', 'external internal mode')


ServiceName = namedtuple('ServiceName', 'project service number')


ConvergencePlan = namedtuple('ConvergencePlan', 'action containers')


@enum.unique
class ConvergenceStrategy(enum.Enum):
    """Enumeration for all possible convergence strategies. Values refer to
    when containers should be recreated.
    """
    changed = 1
    always = 2
    never = 3

    @property
    def allows_recreate(self):
        return self is not type(self).never


class Service(object):
    def __init__(
        self,
        name,
        client=None,
        project='default',
        links=None,
        volumes_from=None,
        net=None,
        **options
    ):
        if not re.match('^%s+$' % VALID_NAME_CHARS, project):
            raise ConfigError('Invalid project name "%s" - only %s are allowed' % (project, VALID_NAME_CHARS))

        self.name = name
        self.client = client
        self.project = project
        self.links = links or []
        self.volumes_from = volumes_from or []
        self.net = net or Net(None)
        self.options = options

    def containers(self, stopped=False, one_off=False, filters={}):
        filters.update({'label': self.labels(one_off=one_off)})

        containers = list(filter(None, [
            Container.from_ps(self.client, container)
            for container in self.client.containers(
                all=stopped,
                filters=filters)]))

        if not containers:
            check_for_legacy_containers(
                self.client,
                self.project,
                [self.name],
            )

        return containers

    def get_container(self, number=1):
        """Return a :class:`compose.container.Container` for this service. The
        container must be active, and match `number`.
        """
        labels = self.labels() + ['{0}={1}'.format(LABEL_CONTAINER_NUMBER, number)]
        for container in self.client.containers(filters={'label': labels}):
            return Container.from_ps(self.client, container)

        raise ValueError("No container found for %s_%s" % (self.name, number))

    def start(self, **options):
        for c in self.containers(stopped=True):
            self.start_container_if_stopped(c, **options)

    # TODO: remove these functions, project takes care of starting/stopping,
    def stop(self, **options):
        for c in self.containers():
            log.info("Stopping %s" % c.name)
            c.stop(**options)

    def pause(self, **options):
        for c in self.containers(filters={'status': 'running'}):
            log.info("Pausing %s" % c.name)
            c.pause(**options)

    def unpause(self, **options):
        for c in self.containers(filters={'status': 'paused'}):
            log.info("Unpausing %s" % c.name)
            c.unpause()

    def kill(self, **options):
        for c in self.containers():
            log.info("Killing %s" % c.name)
            c.kill(**options)

    def restart(self, **options):
        for c in self.containers():
            log.info("Restarting %s" % c.name)
            c.restart(**options)

    # end TODO

    def scale(self, desired_num, timeout=DEFAULT_TIMEOUT):
        """
        Adjusts the number of containers to the specified number and ensures
        they are running.

        - creates containers until there are at least `desired_num`
        - stops containers until there are at most `desired_num` running
        - starts containers until there are at least `desired_num` running
        - removes all stopped containers
        """
        if self.custom_container_name() and desired_num > 1:
            log.warn('The "%s" service is using the custom container name "%s". '
                     'Docker requires each container to have a unique name. '
                     'Remove the custom name to scale the service.'
                     % (self.name, self.custom_container_name()))

        if self.specifies_host_port():
            log.warn('The "%s" service specifies a port on the host. If multiple containers '
                     'for this service are created on a single host, the port will clash.'
                     % self.name)

        def create_and_start(service, number):
            container = service.create_container(number=number, quiet=True)
            container.start()
            return container

        running_containers = self.containers(stopped=False)
        num_running = len(running_containers)

        if desired_num == num_running:
            # do nothing as we already have the desired number
            log.info('Desired container number already achieved')
            return

        if desired_num > num_running:
            # we need to start/create until we have desired_num
            all_containers = self.containers(stopped=True)

            if num_running != len(all_containers):
                # we have some stopped containers, let's start them up again
                stopped_containers = sorted([c for c in all_containers if not c.is_running], key=attrgetter('number'))

                num_stopped = len(stopped_containers)

                if num_stopped + num_running > desired_num:
                    num_to_start = desired_num - num_running
                    containers_to_start = stopped_containers[:num_to_start]
                else:
                    containers_to_start = stopped_containers

                parallel_execute(
                    objects=containers_to_start,
                    obj_callable=lambda c: c.start(),
                    msg_index=lambda c: c.name,
                    msg="Starting"
                )

                num_running += len(containers_to_start)

            num_to_create = desired_num - num_running
            next_number = self._next_container_number()
            container_numbers = [
                number for number in range(
                    next_number, next_number + num_to_create
                )
            ]

            parallel_execute(
                objects=container_numbers,
                obj_callable=lambda n: create_and_start(service=self, number=n),
                msg_index=lambda n: n,
                msg="Creating and starting"
            )

        if desired_num < num_running:
            num_to_stop = num_running - desired_num
            sorted_running_containers = sorted(running_containers, key=attrgetter('number'))
            containers_to_stop = sorted_running_containers[-num_to_stop:]

            parallel_execute(
                objects=containers_to_stop,
                obj_callable=lambda c: c.stop(timeout=timeout),
                msg_index=lambda c: c.name,
                msg="Stopping"
            )

        self.remove_stopped()

    def remove_stopped(self, **options):
        containers = [c for c in self.containers(stopped=True) if not c.is_running]

        parallel_execute(
            objects=containers,
            obj_callable=lambda c: c.remove(**options),
            msg_index=lambda c: c.name,
            msg="Removing"
        )

    def create_container(self,
                         one_off=False,
                         do_build=True,
                         previous_container=None,
                         number=None,
                         quiet=False,
                         **override_options):
        """
        Create a container for this service. If the image doesn't exist, attempt to pull
        it.
        """
        self.ensure_image_exists(
            do_build=do_build,
        )

        container_options = self._get_container_create_options(
            override_options,
            number or self._next_container_number(one_off=one_off),
            one_off=one_off,
            previous_container=previous_container,
        )

        if 'name' in container_options and not quiet:
            log.info("Creating %s" % container_options['name'])

        return Container.create(self.client, **container_options)

    def ensure_image_exists(self,
                            do_build=True):

        try:
            self.image()
            return
        except NoSuchImageError:
            pass

        if self.can_be_built():
            if do_build:
                self.build()
            else:
                raise NeedsBuildError(self)
        else:
            self.pull()

    def image(self):
        try:
            return self.client.inspect_image(self.image_name)
        except APIError as e:
            if e.response.status_code == 404 and e.explanation and 'No such image' in str(e.explanation):
                raise NoSuchImageError("Image '{}' not found".format(self.image_name))
            else:
                raise

    @property
    def image_name(self):
        if self.can_be_built():
            return self.full_name
        else:
            return self.options['image']

    def convergence_plan(self, strategy=ConvergenceStrategy.changed):
        containers = self.containers(stopped=True)

        if not containers:
            return ConvergencePlan('create', [])

        if strategy is ConvergenceStrategy.never:
            return ConvergencePlan('start', containers)

        if (
            strategy is ConvergenceStrategy.always or
            self._containers_have_diverged(containers)
        ):
            return ConvergencePlan('recreate', containers)

        stopped = [c for c in containers if not c.is_running]

        if stopped:
            return ConvergencePlan('start', stopped)

        return ConvergencePlan('noop', containers)

    def _containers_have_diverged(self, containers):
        config_hash = None

        try:
            config_hash = self.config_hash
        except NoSuchImageError as e:
            log.debug(
                'Service %s has diverged: %s',
                self.name, six.text_type(e),
            )
            return True

        has_diverged = False

        for c in containers:
            container_config_hash = c.labels.get(LABEL_CONFIG_HASH, None)
            if container_config_hash != config_hash:
                log.debug(
                    '%s has diverged: %s != %s',
                    c.name, container_config_hash, config_hash,
                )
                has_diverged = True

        return has_diverged

    def execute_convergence_plan(self,
                                 plan,
                                 do_build=True,
                                 timeout=DEFAULT_TIMEOUT):
        (action, containers) = plan

        if action == 'create':
            container = self.create_container(
                do_build=do_build,
            )
            self.start_container(container)

            return [container]

        elif action == 'recreate':
            return [
                self.recreate_container(
                    c,
                    timeout=timeout
                )
                for c in containers
            ]

        elif action == 'start':
            for c in containers:
                self.start_container_if_stopped(c)

            return containers

        elif action == 'noop':
            for c in containers:
                log.info("%s is up-to-date" % c.name)

            return containers

        else:
            raise Exception("Invalid action: {}".format(action))

    def recreate_container(self,
                           container,
                           timeout=DEFAULT_TIMEOUT):
        """Recreate a container.

        The original container is renamed to a temporary name so that data
        volumes can be copied to the new container, before the original
        container is removed.
        """
        log.info("Recreating %s" % container.name)
        try:
            container.stop(timeout=timeout)
        except APIError as e:
            if (e.response.status_code == 500
                    and e.explanation
                    and 'no such process' in str(e.explanation)):
                pass
            else:
                raise

        # Use a hopefully unique container name by prepending the short id
        self.client.rename(
            container.id,
            '%s_%s' % (container.short_id, container.name))

        new_container = self.create_container(
            do_build=False,
            previous_container=container,
            number=container.labels.get(LABEL_CONTAINER_NUMBER),
            quiet=True,
        )
        self.start_container(new_container)
        container.remove()
        return new_container

    def start_container_if_stopped(self, container):
        if container.is_running:
            return container
        else:
            log.info("Starting %s" % container.name)
            return self.start_container(container)

    def start_container(self, container):
        container.start()
        return container

    def remove_duplicate_containers(self, timeout=DEFAULT_TIMEOUT):
        for c in self.duplicate_containers():
            log.info('Removing %s' % c.name)
            c.stop(timeout=timeout)
            c.remove()

    def duplicate_containers(self):
        containers = sorted(
            self.containers(stopped=True),
            key=lambda c: c.get('Created'),
        )

        numbers = set()

        for c in containers:
            if c.number in numbers:
                yield c
            else:
                numbers.add(c.number)

    @property
    def config_hash(self):
        return json_hash(self.config_dict())

    def config_dict(self):
        return {
            'options': self.options,
            'image_id': self.image()['Id'],
            'links': self.get_link_names(),
            'net': self.net.id,
            'volumes_from': self.get_volumes_from_names(),
        }

    def get_dependency_names(self):
        net_name = self.net.service_name
        return (self.get_linked_service_names() +
                self.get_volumes_from_names() +
                ([net_name] if net_name else []))

    def get_linked_service_names(self):
        return [service.name for (service, _) in self.links]

    def get_link_names(self):
        return [(service.name, alias) for service, alias in self.links]

    def get_volumes_from_names(self):
        return [s.name for s in self.volumes_from if isinstance(s, Service)]

    def get_container_name(self, number, one_off=False):
        # TODO: Implement issue #652 here
        return build_container_name(self.project, self.name, number, one_off)

    # TODO: this would benefit from github.com/docker/docker/pull/11943
    # to remove the need to inspect every container
    def _next_container_number(self, one_off=False):
        containers = filter(None, [
            Container.from_ps(self.client, container)
            for container in self.client.containers(
                all=True,
                filters={'label': self.labels(one_off=one_off)})
        ])
        numbers = [c.number for c in containers]
        return 1 if not numbers else max(numbers) + 1

    def _get_links(self, link_to_self):
        links = []
        for service, link_name in self.links:
            for container in service.containers():
                links.append((container.name, link_name or service.name))
                links.append((container.name, container.name))
                links.append((container.name, container.name_without_project))
        if link_to_self:
            for container in self.containers():
                links.append((container.name, self.name))
                links.append((container.name, container.name))
                links.append((container.name, container.name_without_project))
        for external_link in self.options.get('external_links') or []:
            if ':' not in external_link:
                link_name = external_link
            else:
                external_link, link_name = external_link.split(':')
            links.append((external_link, link_name))
        return links

    def _get_volumes_from(self):
        volumes_from = []
        for volume_source in self.volumes_from:
            if isinstance(volume_source, Service):
                containers = volume_source.containers(stopped=True)
                if not containers:
                    volumes_from.append(volume_source.create_container().id)
                else:
                    volumes_from.extend(map(attrgetter('id'), containers))

            elif isinstance(volume_source, Container):
                volumes_from.append(volume_source.id)

        return volumes_from

    def _get_container_create_options(
            self,
            override_options,
            number,
            one_off=False,
            previous_container=None):
        add_config_hash = (not one_off and not override_options)

        container_options = dict(
            (k, self.options[k])
            for k in DOCKER_CONFIG_KEYS if k in self.options)
        container_options.update(override_options)

        if self.custom_container_name() and not one_off:
            container_options['name'] = self.custom_container_name()
        elif not container_options.get('name'):
            container_options['name'] = self.get_container_name(number, one_off)

        if 'detach' not in container_options:
            container_options['detach'] = True

        # If a qualified hostname was given, split it into an
        # unqualified hostname and a domainname unless domainname
        # was also given explicitly. This matches the behavior of
        # the official Docker CLI in that scenario.
        if ('hostname' in container_options
                and 'domainname' not in container_options
                and '.' in container_options['hostname']):
            parts = container_options['hostname'].partition('.')
            container_options['hostname'] = parts[0]
            container_options['domainname'] = parts[2]

        if 'ports' in container_options or 'expose' in self.options:
            ports = []
            all_ports = container_options.get('ports', []) + self.options.get('expose', [])
            for port_range in all_ports:
                internal_range, _ = split_port(port_range)
                for port in internal_range:
                    port = str(port)
                    if '/' in port:
                        port = tuple(port.split('/'))
                    ports.append(port)
            container_options['ports'] = ports

        override_options['binds'] = merge_volume_bindings(
            container_options.get('volumes') or [],
            previous_container)

        if 'volumes' in container_options:
            container_options['volumes'] = dict(
                (parse_volume_spec(v).internal, {})
                for v in container_options['volumes'])

        container_options['environment'] = merge_environment(
            self.options.get('environment'),
            override_options.get('environment'))

        if previous_container:
            container_options['environment']['affinity:container'] = ('=' + previous_container.id)

        container_options['image'] = self.image_name

        container_options['labels'] = build_container_labels(
            container_options.get('labels', {}),
            self.labels(one_off=one_off),
            number,
            self.config_hash if add_config_hash else None)

        # Delete options which are only used when starting
        for key in DOCKER_START_KEYS:
            container_options.pop(key, None)

        container_options['host_config'] = self._get_container_host_config(
            override_options,
            one_off=one_off)

        return container_options

    def _get_container_host_config(self, override_options, one_off=False):
        options = dict(self.options, **override_options)
        port_bindings = build_port_bindings(options.get('ports') or [])

        privileged = options.get('privileged', False)
        cap_add = options.get('cap_add', None)
        cap_drop = options.get('cap_drop', None)
        log_config = LogConfig(
            type=options.get('log_driver', ""),
            config=options.get('log_opt', None)
        )
        pid = options.get('pid', None)
        security_opt = options.get('security_opt', None)

        dns = options.get('dns', None)
        if isinstance(dns, six.string_types):
            dns = [dns]

        dns_search = options.get('dns_search', None)
        if isinstance(dns_search, six.string_types):
            dns_search = [dns_search]

        restart = parse_restart_spec(options.get('restart', None))

        extra_hosts = build_extra_hosts(options.get('extra_hosts', None))
        read_only = options.get('read_only', None)

        devices = options.get('devices', None)

        return self.client.create_host_config(
            links=self._get_links(link_to_self=one_off),
            port_bindings=port_bindings,
            binds=options.get('binds'),
            volumes_from=self._get_volumes_from(),
            privileged=privileged,
            network_mode=self.net.mode,
            devices=devices,
            dns=dns,
            dns_search=dns_search,
            restart_policy=restart,
            cap_add=cap_add,
            cap_drop=cap_drop,
            mem_limit=options.get('mem_limit'),
            memswap_limit=options.get('memswap_limit'),
            log_config=log_config,
            extra_hosts=extra_hosts,
            read_only=read_only,
            pid_mode=pid,
            security_opt=security_opt,
            ipc_mode=options.get('ipc')
        )

    def build(self, no_cache=False, pull=False):
        log.info('Building %s' % self.name)

        path = self.options['build']
        # python2 os.path() doesn't support unicode, so we need to encode it to
        # a byte string
        if not six.PY3:
            path = path.encode('utf8')

        build_output = self.client.build(
            path=path,
            tag=self.image_name,
            stream=True,
            rm=True,
            pull=pull,
            nocache=no_cache,
            dockerfile=self.options.get('dockerfile', None),
        )

        try:
            all_events = stream_output(build_output, sys.stdout)
        except StreamOutputError as e:
            raise BuildError(self, six.text_type(e))

        # Ensure the HTTP connection is not reused for another
        # streaming command, as the Docker daemon can sometimes
        # complain about it
        self.client.close()

        image_id = None

        for event in all_events:
            if 'stream' in event:
                match = re.search(r'Successfully built ([0-9a-f]+)', event.get('stream', ''))
                if match:
                    image_id = match.group(1)

        if image_id is None:
            raise BuildError(self, event if all_events else 'Unknown')

        return image_id

    def can_be_built(self):
        return 'build' in self.options

    @property
    def full_name(self):
        """
        The tag to give to images built for this service.
        """
        return '%s_%s' % (self.project, self.name)

    def labels(self, one_off=False):
        return [
            '{0}={1}'.format(LABEL_PROJECT, self.project),
            '{0}={1}'.format(LABEL_SERVICE, self.name),
            '{0}={1}'.format(LABEL_ONE_OFF, "True" if one_off else "False")
        ]

    def custom_container_name(self):
        return self.options.get('container_name')

    def specifies_host_port(self):
        for port in self.options.get('ports', []):
            if ':' in str(port):
                return True
        return False

    def pull(self, ignore_pull_failures=False):
        if 'image' not in self.options:
            return

        repo, tag, separator = parse_repository_tag(self.options['image'])
        tag = tag or 'latest'
        log.info('Pulling %s (%s%s%s)...' % (self.name, repo, separator, tag))
        output = self.client.pull(
            repo,
            tag=tag,
            stream=True,
        )

        try:
            stream_output(output, sys.stdout)
        except StreamOutputError as e:
            if not ignore_pull_failures:
                raise
            else:
                log.error(six.text_type(e))


class Net(object):
    """A `standard` network mode (ex: host, bridge)"""

    service_name = None

    def __init__(self, net):
        self.net = net

    @property
    def id(self):
        return self.net

    mode = id


class ContainerNet(object):
    """A network mode that uses a container's network stack."""

    service_name = None

    def __init__(self, container):
        self.container = container

    @property
    def id(self):
        return self.container.id

    @property
    def mode(self):
        return 'container:' + self.container.id


class ServiceNet(object):
    """A network mode that uses a service's network stack."""

    def __init__(self, service):
        self.service = service

    @property
    def id(self):
        return self.service.name

    service_name = id

    @property
    def mode(self):
        containers = self.service.containers()
        if containers:
            return 'container:' + containers[0].id

        log.warn("Warning: Service %s is trying to use reuse the network stack "
                 "of another service that is not running." % (self.id))
        return None


# Names


def build_container_name(project, service, number, one_off=False):
    bits = [project, service]
    if one_off:
        bits.append('run')
    return '_'.join(bits + [str(number)])


# Images

def parse_repository_tag(repo_path):
    """Splits image identification into base image path, tag/digest
    and it's separator.

    Example:

    >>> parse_repository_tag('user/repo@sha256:digest')
    ('user/repo', 'sha256:digest', '@')
    >>> parse_repository_tag('user/repo:v1')
    ('user/repo', 'v1', ':')
    """
    tag_separator = ":"
    digest_separator = "@"

    if digest_separator in repo_path:
        repo, tag = repo_path.rsplit(digest_separator, 1)
        return repo, tag, digest_separator

    repo, tag = repo_path, ""
    if tag_separator in repo_path:
        repo, tag = repo_path.rsplit(tag_separator, 1)
        if "/" in tag:
            repo, tag = repo_path, ""

    return repo, tag, tag_separator


# Volumes


def merge_volume_bindings(volumes_option, previous_container):
    """Return a list of volume bindings for a container. Container data volumes
    are replaced by those from the previous container.
    """
    volume_bindings = dict(
        build_volume_binding(parse_volume_spec(volume))
        for volume in volumes_option or []
        if ':' in volume)

    if previous_container:
        volume_bindings.update(
            get_container_data_volumes(previous_container, volumes_option))

    return list(volume_bindings.values())


def get_container_data_volumes(container, volumes_option):
    """Find the container data volumes that are in `volumes_option`, and return
    a mapping of volume bindings for those volumes.
    """
    volumes = []

    volumes_option = volumes_option or []
    container_volumes = container.get('Volumes') or {}
    image_volumes = container.image_config['ContainerConfig'].get('Volumes') or {}

    for volume in set(volumes_option + list(image_volumes)):
        volume = parse_volume_spec(volume)
        # No need to preserve host volumes
        if volume.external:
            continue

        volume_path = container_volumes.get(volume.internal)
        # New volume, doesn't exist in the old container
        if not volume_path:
            continue

        # Copy existing volume from old container
        volume = volume._replace(external=volume_path)
        volumes.append(build_volume_binding(volume))

    return dict(volumes)


def build_volume_binding(volume_spec):
    return volume_spec.internal, "{}:{}:{}".format(*volume_spec)


def parse_volume_spec(volume_config):
    """
    A volume_config string, which is a path, split it into external:internal[:mode]
    parts to be returned as a valid VolumeSpec tuple.
    """
    parts = volume_config.split(':')

    if IS_WINDOWS_PLATFORM:
        # relative paths in windows expand to include the drive, eg C:\
        # so we join the first 2 parts back together to count as one
        drive, volume_path = os.path.splitdrive(volume_config)
        windows_parts = volume_path.split(":")
        windows_parts[0] = os.path.join(drive, windows_parts[0])
        parts = windows_parts

    if len(parts) > 3:
        raise ConfigError("Volume %s has incorrect format, should be "
                          "external:internal[:mode]" % volume_config)

    if len(parts) == 1:
        external = None
        internal = os.path.normpath(parts[0])
    else:
        external = os.path.normpath(parts[0])
        internal = os.path.normpath(parts[1])

    mode = parts[2] if len(parts) == 3 else 'rw'

    return VolumeSpec(external, internal, mode)

# Labels


def build_container_labels(label_options, service_labels, number, config_hash):
    labels = dict(label_options or {})
    labels.update(label.split('=', 1) for label in service_labels)
    labels[LABEL_CONTAINER_NUMBER] = str(number)
    labels[LABEL_VERSION] = __version__

    if config_hash:
        log.debug("Added config hash: %s" % config_hash)
        labels[LABEL_CONFIG_HASH] = config_hash

    return labels


# Restart policy


def parse_restart_spec(restart_config):
    if not restart_config:
        return None
    parts = restart_config.split(':')
    if len(parts) > 2:
        raise ConfigError("Restart %s has incorrect format, should be "
                          "mode[:max_retry]" % restart_config)
    if len(parts) == 2:
        name, max_retry_count = parts
    else:
        name, = parts
        max_retry_count = 0

    return {'Name': name, 'MaximumRetryCount': int(max_retry_count)}


# Extra hosts


def build_extra_hosts(extra_hosts_config):
    if not extra_hosts_config:
        return {}

    if isinstance(extra_hosts_config, list):
        extra_hosts_dict = {}
        for extra_hosts_line in extra_hosts_config:
            if not isinstance(extra_hosts_line, six.string_types):
                raise ConfigError(
                    "extra_hosts_config \"%s\" must be either a list of strings or a string->string mapping," %
                    extra_hosts_config
                )
            host, ip = extra_hosts_line.split(':')
            extra_hosts_dict.update({host.strip(): ip.strip()})
        extra_hosts_config = extra_hosts_dict

    if isinstance(extra_hosts_config, dict):
        return extra_hosts_config

    raise ConfigError(
        "extra_hosts_config \"%s\" must be either a list of strings or a string->string mapping," %
        extra_hosts_config
    )