docker-py是Docker SDK for Python。docker-py主要利用了requests，使用http/socket协议连接本地的docker engine进行操作。对 docker 感兴趣，苦于工作中只用到 http 协议的同学，都建议阅读一下本文。话不多数，一起了解docker-py的实现，本文分下面几个部分:
- docker-py项目结构
- docker-py API示例
- DockerClient的实现
- docker-version命令跟踪
- UnixHTTPAdapter的实现
- docker-ps命令跟踪
- docker-logs命令跟踪
- docker-exec 命令跟踪
- 小结
- 小技巧
docker-py项目结构
本次代码阅读，使用的版本是 4.2.0， 项目目录结构大概如下:
| 文件 |
描述 |
| client.py |
docker客户端的API |
| api |
api相关目录 |
| api/client.py |
api的主要实现 |
| api/container.py |
container相关的api和client-mixin |
| api/daemon.py |
daemon相关的api和client-mixin |
| models |
下为各种对象模型，主要是单体及集合 |
| models/resource.py |
模型基类 |
| models/containers.py |
Container和ContainerCollection模型 |
| transport |
为客户端和服务端的交互协议 |
| transport/unixconn.py |
mac下主要使用了unix-sock实现 |
还有一些目录和类，因为不在这次介绍中，所以就没有罗列。
docker-py API示例
docker-py API上手非常简单:
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import docker
client = docker.from_env()
result = client.version()
print(result)
# {'Platform': {'Name': 'Docker Engine - Community'},...}
client.containers.list()
# [<Container '45e6d2de7c54'>, <Container 'db18e4f20eaa'>, ...]
client.images.pull('nginx:1.10-alpine')
# <Image: 'nginx:1.10-alpine'>
client.images.list()
[<Image 'ubuntu'>, <Image 'nginx:1.10-alpine'>, ...]
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上面示例展示了:
- 使用环境变量，创建client连接本地
docker-engine服务
- 获取版本号，等同
docker version
- 获取正在运行的容器列表，等同
docker container list(别名是 docker ps)
- 拉取 nginx:1.10-alpin 镜像，等同
docker image pull nginx:1.10-alpine(别名是docker pull nginx:1.10-alpine)
- 获取镜像列表, 等同
docker image list
我们可以看到，docker-py的操作和docker的标准命令基本一致。
DockerClient的实现
DockerClient的构造函数和工厂方法展示docker-client对象包装了APIClient对象：
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# client.py
class DockerClient(object):
def __init__(self, *args, **kwargs):
self.api = APIClient(*args, **kwargs)
@classmethod
def from_env(cls, **kwargs):
timeout = kwargs.pop('timeout', DEFAULT_TIMEOUT_SECONDS)
max_pool_size = kwargs.pop('max_pool_size', DEFAULT_MAX_POOL_SIZE)
version = kwargs.pop('version', None)
use_ssh_client = kwargs.pop('use_ssh_client', False)
return cls(
timeout=timeout,
max_pool_size=max_pool_size,
version=version,
use_ssh_client=use_ssh_client,
**kwargs_from_env(**kwargs)
)
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DockerClient的API分2中，一种是属性方法，比如常用的 containers，images，networks 和 volumes 等子命令，因为要将返回值包装成对应模型对象:
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@property
def containers(self):
"""
An object for managing containers on the server. See the
:doc:`containers documentation <containers>` for full details.
"""
return ContainerCollection(client=self)
@property
def images(self):
return ImageCollection(client=self)
@property
def networks(self):
return NetworkCollection(client=self)
@property
def volumes(self):
return VolumeCollection(client=self)
...
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另一种是不需要模型包装，可以直接使用APIClient返回结果的 info, version 等方法:
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# Top-level methods
def info(self, *args, **kwargs):
return self.api.info(*args, **kwargs)
info.__doc__ = APIClient.info.__doc__
def version(self, *args, **kwargs):
return self.api.version(*args, **kwargs)
version.__doc__ = APIClient.version.__doc__
...
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DockerClient类工厂方法的全局引用:
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from_env = DockerClient.from_env
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docker-version命令跟踪
我们先从简单的 docker version 命令跟踪查看APIClient如何工作的。APIClient的构造函数:
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# api/client.py
import requests
class APIClient(
requests.Session,
BuildApiMixin,
ConfigApiMixin,
ContainerApiMixin,
DaemonApiMixin,
ExecApiMixin,
ImageApiMixin,
NetworkApiMixin,
PluginApiMixin,
SecretApiMixin,
ServiceApiMixin,
SwarmApiMixin,
VolumeApiMixin):
def __init__(self, base_url=None, version=None,
timeout=DEFAULT_TIMEOUT_SECONDS, tls=False,
user_agent=DEFAULT_USER_AGENT, num_pools=None,
credstore_env=None, use_ssh_client=False,
max_pool_size=DEFAULT_MAX_POOL_SIZE):
super(APIClient, self).__init__()
base_url = utils.parse_host(
base_url, IS_WINDOWS_PLATFORM, tls=bool(tls)
)
if base_url.startswith('http+unix://'):
self._custom_adapter = UnixHTTPAdapter(
base_url, timeout, pool_connections=num_pools,
max_pool_size=max_pool_size
)
self.mount('http+docker://', self._custom_adapter)
self._unmount('http://', 'https://')
# host part of URL should be unused, but is resolved by requests
# module in proxy_bypass_macosx_sysconf()
self.base_url = 'http+docker://localhost'
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上面代码可见:
- APIClient继承自 requests.Session
- APIClient使用Mixin方式组合了多个API，比如ContainerApiMixin提供container的api操作;NetWorkApiMixin提供network的api操作
- 使用mount方法加载不同协议的适配器adapter，unix系的docker是unix-socket;windows则是npipe
关于requests的使用，可以参看之前的博文 requests 源码阅读
默认的服务URL实现:
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DEFAULT_UNIX_SOCKET = "http+unix:///var/run/docker.sock"
DEFAULT_NPIPE = 'npipe:////./pipe/docker_engine'
def parse_host(addr, is_win32=False, tls=False):
path = ''
port = None
host = None
# Sensible defaults
if not addr and is_win32:
return DEFAULT_NPIPE
if not addr or addr.strip() == 'unix://':
return DEFAULT_UNIX_SOCKET
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version 请求在 DaemonApiMixin 中实现:
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class DaemonApiMixin(object):
def version(self, api_version=True):
url = self._url("/version", versioned_api=api_version)
return self._result(self._get(url), json=True)
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底层的请求和响应在主类APIClient中提供:
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class APIClient
def _url(self, pathfmt, *args, **kwargs):
...
return '{0}{1}'.format(self.base_url, pathfmt.format(*args))
@update_headers
def _get(self, url, **kwargs):
return self.get(url, **self._set_request_timeout(kwargs))
def _result(self, response, json=False, binary=False):
assert not (json and binary)
self._raise_for_status(response)
if json:
return response.json()
if binary:
return response.content
return response.text
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get和result，response都是requests提供。get发送请求，response.json将请求格式化成json后返回。
UnixHTTPAdapter的实现
/var/run/docker.sock是Docker守护程序侦听的UNIX套接字,其连接使用UnixHTTPAdapter处理:
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# transport/unixconn.py
import requests.adapters
RecentlyUsedContainer = urllib3._collections.RecentlyUsedContainer
class UnixHTTPAdapter(BaseHTTPAdapter):
def __init__(self, socket_url, timeout=60,
pool_connections=constants.DEFAULT_NUM_POOLS,
max_pool_size=constants.DEFAULT_MAX_POOL_SIZE):
socket_path = socket_url.replace('http+unix://', '')
if not socket_path.startswith('/'):
socket_path = '/' + socket_path
self.socket_path = socket_path
self.timeout = timeout
self.max_pool_size = max_pool_size
self.pools = RecentlyUsedContainer(
pool_connections, dispose_func=lambda p: p.close()
)
super(UnixHTTPAdapter, self).__init__()
def get_connection(self, url, proxies=None):
with self.pools.lock:
pool = self.pools.get(url)
if pool:
return pool
pool = UnixHTTPConnectionPool(
url, self.socket_path, self.timeout,
maxsize=self.max_pool_size
)
self.pools[url] = pool
return pool
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UnixHTTPAdapter主要使用urllib3提供的链接池管理UnixHTTPConnection连接:
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class UnixHTTPConnection(httplib.HTTPConnection, object):
def __init__(self, base_url, unix_socket, timeout=60):
super(UnixHTTPConnection, self).__init__(
'localhost', timeout=timeout
)
self.base_url = base_url
self.unix_socket = unix_socket
self.timeout = timeout
self.disable_buffering = False
def connect(self):
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
sock.settimeout(self.timeout)
sock.connect(self.unix_socket)
self.sock = sock
def putheader(self, header, *values):
super(UnixHTTPConnection, self).putheader(header, *values)
if header == 'Connection' and 'Upgrade' in values:
self.disable_buffering = True
def response_class(self, sock, *args, **kwargs):
if self.disable_buffering:
kwargs['disable_buffering'] = True
return UnixHTTPResponse(sock, *args, **kwargs)
class UnixHTTPConnectionPool(urllib3.connectionpool.HTTPConnectionPool):
def __init__(self, base_url, socket_path, timeout=60, maxsize=10):
super(UnixHTTPConnectionPool, self).__init__(
'localhost', timeout=timeout, maxsize=maxsize
)
self.base_url = base_url
self.socket_path = socket_path
self.timeout = timeout
def _new_conn(self):
return UnixHTTPConnection(
self.base_url, self.socket_path, self.timeout
)
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connect展示了socket类型是 socket.AF_UNIX, 这一部分的实现都非常基础 。
关于socket，可以参看之前的博文 python http 源码阅读
docker-ps命令跟踪
接着我们跟踪稍微复杂点的命令 client.containers.list()， 也就是 docker ps。前面介绍了，container 会组装结果为数据模型，下面是模型的父类:
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class Model(object):
"""
A base class for representing a single object on the server.
"""
id_attribute = 'Id'
def __init__(self, attrs=None, client=None, collection=None):
self.client = client
# 集合
self.collection = collection
self.attrs = attrs
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Model是单个模型抽象，Collection则是模型集合的抽象，使用集合的prepare_model构建各种对象:
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class Collection(object):
"""
A base class for representing all objects of a particular type on the
server.
"""
model = None
def __init__(self, client=None):
self.client = client
...
def prepare_model(self, attrs):
"""
Create a model from a set of attributes.
"""
if isinstance(attrs, Model):
attrs.client = self.client
# 双向引用
attrs.collection = self
return attrs
elif isinstance(attrs, dict):
return self.model(attrs=attrs, client=self.client, collection=self)
else:
raise Exception("Can't create %s from %s" %
(self.model.__name__, attrs))
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Container和ContainerCollection的实现
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class Container(Model):
pass
class ContainerCollection(Collection):
model = Container
def get(self, container_id):
resp = self.client.api.inspect_container(container_id)
return self.prepare_model(resp)
def list(self, all=False, before=None, filters=None, limit=-1, since=None,
sparse=False, ignore_removed=False):
resp = self.client.api.containers(all=all, before=before,
filters=filters, limit=limit,
since=since)
containers = []
for r in resp:
containers.append(self.get(r['Id']))
return containers
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其中list函数主要有下面几个步骤
- 使用api的containers接口得到resp，就是container-id列表
- 逐个循环使用api的inspect_container请求container的详细信息
- 将结果封装成Container对象
- 返回容器Container对象列表
api.containers和api.inspect_container在ContainerApiMixin中提供, 非常简单清晰:
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class ContainerApiMixin(object):
def containers(self, quiet=False, all=False, trunc=False, latest=False,
since=None, before=None, limit=-1, size=False,
filters=None):
params = {
'limit': 1 if latest else limit,
'all': 1 if all else 0,
'size': 1 if size else 0,
'trunc_cmd': 1 if trunc else 0,
'since': since,
'before': before
}
if filters:
params['filters'] = utils.convert_filters(filters)
u = self._url("/containers/json")
res = self._result(self._get(u, params=params), True)
if quiet:
return [{'Id': x['Id']} for x in res]
if trunc:
for x in res:
x['Id'] = x['Id'][:12]
return res
@utils.check_resource('container')
def inspect_container(self, container):
return self._result(
self._get(self._url("/containers/{0}/json", container)), True
)
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docker-logs命令跟踪
前面的命令都是request-response的模式，我们再看看不一样的，基于流的docker-logs命令。我们先启动一个容器:
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docker run -d bfirsh/reticulate-splines
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查看容器列表
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# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
61709b0ed4b8 bfirsh/reticulate-splines "/usr/local/bin/run.…" 22 seconds ago Up 21 seconds festive_pare
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实时跟踪容器运行日志:
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# docker logs -f 6170
Reticulating spline 1...
Reticulating spline 2...
....
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可以看到reticulate-splines容器就是不停的打印行数数据。可以用下面的代码实现 docker logs 相同的功能:
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logs = client.containers.get('61709b0ed4b8').logs(stream=True)
try:
while True:
line = next(logs).decode("utf-8")
print(line)
except StopIteration:
print(f'log stream ended for {container_name}')
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代码执行结果和前面的类似:
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# python sample.py
...
Reticulating spline 14...
Reticulating spline 15...
...
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logs的实现中返回一个CancellableStream，而不是一个result，利用这个stream，就可以持续的读取输出:
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# models/Container
def logs(self, **kwargs):
return self.client.api.logs(self.id, **kwargs)
# api/continer
def logs(self, container, stdout=True, stderr=True, stream=False,
timestamps=False, tail='all', since=None, follow=None,
until=None):
...
url = self._url("/containers/{0}/logs", container)
res = self._get(url, params=params, stream=stream)
output = self._get_result(container, stream, res)
if stream:
return CancellableStream(output, res)
else:
return output
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比较特别的是下面对于stream的处理:
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# api/client
def _multiplexed_response_stream_helper(self, response):
"""A generator of multiplexed data blocks coming from a response
stream."""
# Disable timeout on the underlying socket to prevent
# Read timed out(s) for long running processes
socket = self._get_raw_response_socket(response)
self._disable_socket_timeout(socket)
while True:
header = response.raw.read(STREAM_HEADER_SIZE_BYTES)
if not header:
break
_, length = struct.unpack('>BxxxL', header)
if not length:
continue
data = response.raw.read(length)
if not data:
break
yield data
def _disable_socket_timeout(self, socket):
sockets = [socket, getattr(socket, '_sock', None)]
for s in sockets:
if not hasattr(s, 'settimeout'):
continue
timeout = -1
if hasattr(s, 'gettimeout'):
timeout = s.gettimeout()
# Don't change the timeout if it is already disabled.
if timeout is None or timeout == 0.0:
continue
s.settimeout(None)
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上面代码展示了:
- 流的读取方式是每次读取STREAM_HEADER_SIZE_BYTES长度的数据作为协议头
- 协议头结构体格式解压后得到后面的数据包长度
- 继续读取指定长度的数据包
- 重复执行上面的数据读取过程
- 流式读取的时候还需要关闭socket的超时机制，确保流一直保持，知道手动(ctl+c)关闭
而 attach 则是采用了websocket的实现, 因为我们一般推荐使用exec命令，所以这里简单了解即可:
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def _attach_websocket(self, container, params=None):
url = self._url("/containers/{0}/attach/ws", container)
req = requests.Request("POST", url, params=self._attach_params(params))
full_url = req.prepare().url
full_url = full_url.replace("http://", "ws://", 1)
full_url = full_url.replace("https://", "wss://", 1)
return self._create_websocket_connection(full_url)
def _create_websocket_connection(self, url):
return websocket.create_connection(url)
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docker-exec 命令跟踪
docker-exec是我们的重头戏，因为除了可以直接获取docker是输出外，还可以和docker进行交互。先简单回顾一下exec的使用:
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# docker exec -it 2075 ping www.weibo.cn
PING www.weibo.cn (123.125.22.241): 56 data bytes
64 bytes from 123.125.22.241: seq=0 ttl=37 time=6.797 ms
64 bytes from 123.125.22.241: seq=1 ttl=37 time=39.279 ms
64 bytes from 123.125.22.241: seq=2 ttl=37 time=29.635 ms
64 bytes from 123.125.22.241: seq=3 ttl=37 time=27.737 ms
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上面示例可以用下面代码完全模拟:
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result = client.containers.get("2075").exec_run("ping www.weibo.cn", tty=True, stream=True)
try:
while True:
line = next(result[1]).decode("utf-8")
print(line)
except StopIteration:
print(f'exec stream ended for {container_name}')
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使用tty伪装终端和容器进行交互，就是我们最常用的方式了:
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# docker exec -it 2075 sh
/ # ls -la
total 64
drwxr-xr-x 1 root root 4096 Mar 24 13:16 .
drwxr-xr-x 1 root root 4096 Mar 24 13:16 ..
-rwxr-xr-x 1 root root 0 Mar 24 13:16 .dockerenv
drwxr-xr-x 2 root root 4096 Mar 3 2017 bin
drwxr-xr-x 5 root root 340 Mar 24 13:16 dev
drwxr-xr-x 1 root root 4096 Mar 24 13:16 etc
drwxr-xr-x 2 root root 4096 Mar 3 2017 home
drwxr-xr-x 1 root root 4096 Mar 3 2017 lib
lrwxrwxrwx 1 root root 12 Mar 3 2017 linuxrc -> /bin/busybox
drwxr-xr-x 5 root root 4096 Mar 3 2017 media
drwxr-xr-x 2 root root 4096 Mar 3 2017 mnt
dr-xr-xr-x 156 root root 0 Mar 24 13:16 proc
drwx------ 1 root root 4096 Mar 25 08:17 root
drwxr-xr-x 2 root root 4096 Mar 3 2017 run
drwxr-xr-x 2 root root 4096 Mar 3 2017 sbin
drwxr-xr-x 2 root root 4096 Mar 3 2017 srv
dr-xr-xr-x 13 root root 0 Mar 24 13:16 sys
drwxrwxrwt 1 root root 4096 Mar 3 2017 tmp
drwxr-xr-x 1 root root 4096 Mar 3 2017 usr
drwxr-xr-x 1 root root 4096 Mar 3 2017 var
/ # exit
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同样这个过程也可以使用docker-py实现:
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_, socket = client.containers.get("2075").exec_run("sh", stdin=True, socket=True)
print(socket)
socket._sock.sendall(b"ls -la\n")
try:
unknown_byte=socket._sock.recv(docker.constants.STREAM_HEADER_SIZE_BYTES)
print(unknown_byte)
buffer_size = 4096 # 4 KiB
data = b''
while True:
part = socket._sock.recv(buffer_size)
data += part
if len(part) < buffer_size:
# either 0 or end of data
break
print(data.decode("utf8"))
except Exception:
pass
socket._sock.send(b"exit\n")
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示例演示的过程是:
- 获取一个已经存在的容器2075
- 对容器执行exec命令，注意需要开启stdin和socket
- 向容器发送
ls -lah 展示目录列表
- 读区socket上的结果。(这里我们偷懒，没有解析头，直接硬取，这样不够健壮)
- 继续发送
exit 退出容器
程序的输出和上面使用命令方式完全一致，就不在张贴了。进入核心的exec_run函数的实现:
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# model/containers
def exec_run(self, cmd, stdout=True, stderr=True, stdin=False, tty=False,
privileged=False, user='', detach=False, stream=False,
socket=False, environment=None, workdir=None, demux=False):
resp = self.client.api.exec_create(
self.id, cmd, stdout=stdout, stderr=stderr, stdin=stdin, tty=tty,
privileged=privileged, user=user, environment=environment,
workdir=workdir,
)
exec_output = self.client.api.exec_start(
resp['Id'], detach=detach, tty=tty, stream=stream, socket=socket,
demux=demux
)
if socket or stream:
return ExecResult(None, exec_output)
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主要使用API的exec_create和exec_start两个函数, 先看第一个exec_create函数:
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# api/exec_api
def exec_create(self, container, cmd, stdout=True, stderr=True,
stdin=False, tty=False, privileged=False, user='',
environment=None, workdir=None, detach_keys=None):
if isinstance(cmd, six.string_types):
cmd = utils.split_command(cmd)
if isinstance(environment, dict):
environment = utils.utils.format_environment(environment)
data = {
'Container': container,
'User': user,
'Privileged': privileged,
'Tty': tty,
'AttachStdin': stdin,
'AttachStdout': stdout,
'AttachStderr': stderr,
'Cmd': cmd,
'Env': environment,
}
if detach_keys:
data['detachKeys'] = detach_keys
elif 'detachKeys' in self._general_configs:
data['detachKeys'] = self._general_configs['detachKeys']
url = self._url('/containers/{0}/exec', container)
res = self._post_json(url, data=data)
return self._result(res, True)
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exec_create相对还是比较简单，就是post-json数据到 /containers/{0}/exec 接口。然后是exec_start函数:
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def exec_start(self, exec_id, detach=False, tty=False, stream=False,
socket=False, demux=False):
# we want opened socket if socket == True
data = {
'Tty': tty,
'Detach': detach
}
headers = {} if detach else {
'Connection': 'Upgrade',
'Upgrade': 'tcp'
}
res = self._post_json(
self._url('/exec/{0}/start', exec_id),
headers=headers,
data=data,
stream=True
)
if detach:
return self._result(res)
if socket:
return self._get_raw_response_socket(res)
return self._read_from_socket(res, stream, tty=tty, demux=demux)
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exec_start是post-json到 /exec/{0}/start 接口，注意这个接口看起来不是到容器，而是到exec。 然后如果socket参数是true则返回socket，可以进行写入；否则仅仅读取数据。
使用curl访问docker-api
docker-engine的REST-api也可以直接使用 curl 访问:
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$ curl --unix-socket /var/run/docker.sock -H "Content-Type: application/json" \
-d '{"Image": "alpine", "Cmd": ["echo", "hello world"]}' \
-X POST http://localhost/v1.41/containers/create
{"Id":"1c6594faf5","Warnings":null}
$ curl --unix-socket /var/run/docker.sock -X POST http://localhost/v1.41/containers/1c6594faf5/start
$ curl --unix-socket /var/run/docker.sock -X POST http://localhost/v1.41/containers/1c6594faf5/wait
{"StatusCode":0}
$ curl --unix-socket /var/run/docker.sock "http://localhost/v1.41/containers/1c6594faf5/logs?stdout=1"
hello world
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可以通过修改/etc/docker/daemon.json更改为http服务方式的api
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{
"debug": true,
"hosts": ["tcp://192.168.59.3:2376"]
}
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然后 curl 命令可以直接访问docker的api
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curl http://127.0.0.1:2375/info
curl http://127.0.0.1:2375/version
curl http://127.0.0.1:2375/images/json
curl http://127.0.0.1:2375/images/alpine/json
curl http://127.0.0.1:2375/containers/json
curl http://127.0.0.1:2375/containers/25c5805a06b6/json
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小结
利用docker-py可以完全操作docker，这得益docker提供的REST-api操作。同时也发现requests的设计很强大，不仅仅可以用来做http请求，还可以用来做socket请求。学习docker-py后，相信大家对docker的理解一定有那么一点点加深，也希望下面这张图可以帮助你记忆:
小技巧
使用 check_resource 装饰器，对函数的参数进行预先处理:
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def check_resource(resource_name):
def decorator(f):
@functools.wraps(f)
def wrapped(self, resource_id=None, *args, **kwargs):
if resource_id is None and kwargs.get(resource_name):
resource_id = kwargs.pop(resource_name)
if isinstance(resource_id, dict):
resource_id = resource_id.get('Id', resource_id.get('ID'))
if not resource_id:
raise errors.NullResource(
'Resource ID was not provided'
)
return f(self, resource_id, *args, **kwargs)
return wrapped
return decorator
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代码版本比较工具:
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from distutils.version import StrictVersion
def compare_version(v1, v2):
"""Compare docker versions
>>> v1 = '1.9'
>>> v2 = '1.10'
>>> compare_version(v1, v2)
1
>>> compare_version(v2, v1)
-1
>>> compare_version(v2, v2)
0
"""
s1 = StrictVersion(v1)
s2 = StrictVersion(v2)
if s1 == s2:
return 0
elif s1 > s2:
return -1
else:
return 1
def version_lt(v1, v2):
return compare_version(v1, v2) > 0
def version_gte(v1, v2):
return not version_lt(v1, v2)
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参考链接