一、什么是API

1. API具体是什么？

API这个词在维基百科里解释是这样的：应用程序接口（英语application programming interface，缩写作 API），又称为应用编程接口，就是软件系统不同组成部分衔接的约定。
简单理解就是，我们不同的安卓和系统的手机就要用不同的数据线充电，类似的，程序的接口也是如此。每个程序都有固定对外的标准接口，这个接口由开发这个程序的开发者定义的，你要想连接它们，那么就应该遵循它们的接口标准

2. 什么是REST

现在学习API 经常看到一个词叫REST，英文全称是Representational State Transfer，中文意思叫"表现层状态转化"

2.1. 什么是表现层？

表现层指的是资源的表现层，所谓"资源"，就是网络上的一个具体信息。一个文本，一部电影，一个服务都可以算作一资源表现层的意思其实就是把"资源"具体呈现出来的形式。比如，我们可以通过一个URL连接下载视频，图片等！

2.2. 什么是状态转化？

简单理解就是对资源增删改查
GET、POST、PUT、DELETE（获取，新建，更新，删除）通过这基本的四种方法可以对网络上的资源进行一些状态转化操作

二、Docker API种类

Docker Registry API （docker镜像仓库的api）
Docker Hub API （Docker Hub API是用户管理操作的API）
Docker Remote API （用于控制主机 Docker 服务端的 API）

Docker Remote API

Docker Remote API是由docker守护进程提供的，默认情况下，docker守护进程绑定到一个宿主机的嵌套字里，即unix:///var/run/run/docker.sock

Remote API 的基本操作

编辑/usr/lib/system/system/docker.service 文件,把 Docker 守护进程绑定到该宿主机的所有网络接口的 2375 端口上

ExecStart=/usr/bin/docker-current -d --selinu-enabled -H tcp://0.0.0.0:2375
# systemctl --system daemon-reload

通过 Docker 客户端命令的-H 标志来测试一下刚才的配置是否生效

# docker daemon -H unix:///var/run/docker.sock -H 0.0.0.0:2375
WARN[0000] /!\ DON'T BIND ON ANY IP ADDRESS WITHOUT setting 
-tlsverify IF YOU DON'T KNOW WHAT YOU'RE DOING /!\
WARN[0000] devmapper: Usage of loopback devices is strongly discouraged for 
production use. Please use `--storage-opt dm.thinpooldev` or use `man docker` to refer 
to dm.thinpooldev section. 
WARN[0000] devmapper: Base device already exists and has filesystem xfs on it. 
User specified filesystem will be ignored. 
INFO[0000] [graphdriver] using prior storage driver "devicemapper" 
INFO[0000] Graph migration to content-addressability took 0.00 seconds 
INFO[0000] Firewalld running: false 
INFO[0000] Default bridge （docker0）is assigned with an IP address 
172.17.0.0/16. Daemon option --bip can be used to set a preferred IP address 
INFO[0000] Loading containers: start. 
.
INFO[0000] Loading containers: done. 
INFO[0000] Daemon has completed initialization
INFO[0000] Docker daemon 
commit=3999ccb-unsupported execdriver=native-0.2 graphdriver=devicemapper 
version=1.10.3
INFO[0001] API listen on [::]:2375 
INFO[0001] API listen on /var/run/docker.sock 
# docker -H 127.0.0.1:2375 info
Containers: 1
Running: 1
Paused: 0
Stopped: 0
Images: 22
Server Version: 1.10.3
Storage Driver: devicemapper
Pool Name: docker-253:1-285241608-pool
Pool Blocksize: 65.54 kB
Base Device Size: 10.74 GB
Backing Filesystem: xfs
Data file: /dev/loop0
Metadata file: /dev/loop1
Data Space Used: 5.105 GB
Data Space Total: 107.4 GB
Data Space Available: 90.75 GB
Metadata Space Used: 10.23 MB
Metadata Space Total: 2.147 GB
Metadata Space Available: 2.137 GB
Udev Sync Supported: true
Deferred Removal Enabled: false
Deferred Deletion Enabled: false
Deferred Deleted Device Count: 0
Data loop file: /var/lib/docker/devicemapper/devicemapper/data
WARNING: Usage of loopback devices is strongly discouraged for production 
use. Either use `--storage-opt dm.thinpooldev` or use `--storage-opt 
dm.no_warn_on_loop_devices=true` to suppress this warning.
Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
Library Version: 1.02.135-RHEL7 （2016-09-28）
Execution Driver: native-0.2
Logging Driver: json-file
Plugins: 
Volume: local
Network: host bridge null
Kernel Version: 3.10.0-229.el7.x86_64
Operating System: CentOS Linux 7 （Core）
OSType: linux
Architecture: x86_64
Number of Docker Hooks: 2
CPUs: 1
Total Memory: 1.954 GiB
Name: docker
ID: 
HRBL:3YXE:HAAO:MRAG:NKQO:MZWC:7EVD:Q2QK:UYK6:C7NF:GOYU:ELS
R
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled
Registries: docker.io （secure）

docker_host 环境变量，这样即省掉了每次都需要设置-H 标志的麻烦

# export DOCKER_HOST="tcp://127.0.0.1:2375"

测试 Docker Remote API

通过 Docker 程序建立并确认了与 Docker 守护进程之间的网络连通
性，接着来直接连接到 API

[root@docker ~]# curl http://127.0.0.1:2375/info 
{"ID":"HRBL:3YXE:HAAO:MRAG:NKQO:MZWC:7EVD:Q2QK:UYK6:C7NF:GOYU:EL
SR","Containers":1,"ContainersRunning":1,"ContainersPaused":0,"ContainersStopped":0,"Images":
22,"Driver":"devicemapper","DriverStatus":[["Pool 
Name","docker-253:1-285241608-pool"],["Pool Blocksize","65.54 kB"],["Base Device 
Size","10.74 GB"],["Backing Filesystem","xfs"],["Data file","/dev/loop0"],["Metadata 
file","/dev/loop1"],["Data Space Used","5.106 GB"],["Data Space Total","107.4 GB"],["Data Space 
Available","90.75 GB"],["Metadata Space Used","10.23 MB"],["Metadata Space Total","2.147 
GB"],["Metadata Space Available","2.137 GB"],["Udev Sync Supported","true"],["Deferred 
Removal Enabled","false"],["Deferred Deletion Enabled","false"],["Deferred Deleted Device 
Count","0"],["Data loop file","/var/lib/docker/devicemapper/devicemapper/data"],["Metadata loop 
file","/var/lib/docker/devicemapper/devicemapper/metadata"],["Library Version","1.02.135-RHEL7 
（2016-09-28）
"]],"SystemStatus":null,"Plugins":{"Volume":["local"],"Network":["host","bridge","null"],"Authori
zation":null},"MemoryLimit":true,"SwapLimit":true,"CpuCfsPeriod":true,"CpuCfsQuota":true,"CP
UShares":true,"CPUSet":true,"IPv4Forwarding":true,"BridgeNfIptables":false,"BridgeNfIp6tables"
:false,"Debug":false,"NFd":21,"OomKillDisable":true,"NGoroutines":28,"SystemTime":"2016-12-3
0T03:24:27.654171066Z","ExecutionDriver":"native-0.2","LoggingDriver":"json-file","NEventsLis
tener":0,"KernelVersion":"3.10.0-229.el7.x86_64","PkgVersion":"docker-common-1.10.3-59.el7.Ce
ntOS.x86_64","OperatingSystem":"CentOS Linux 7 （Core）
","OSType":"linux","Architecture":"x86_64","IndexServerAddress":"https://index.docker.io/v1/","I
ndexServerName":"docker.io","RegistryConfig":{"InsecureRegistryCIDRs":["127.0.0.0/8"],"Index
Configs":{"docker.io":{"Name":"docker.io","Mirrors":null,"Secure":true,"Official":true}},"Mirrors
":null},"InitSha1":"2195bfa7012bb8ffc50f899b658b487b565336e1","InitPath":"","NCPU":1,"Mem
Total":2098581504,"DockerRootDir":"/var/lib/docker","HttpProxy":"","HttpsProxy":"","NoProxy":
"","Name":"docker","Labels":null,"ExperimentalBuild":false,"ServerVersion":"1.10.3","ClusterStor
e":"","ClusterAdvertise":"","Registries":[{"Name":"docker.io","Secure":true}]}

通过 API 来管理 Docker 镜像。

获取 Docker 守护进程中所有进程中所有镜像的列表

# curl http://127.0.0.1:2375/images/json | python -m json.tool
 % Total % Received % Xferd Average Speed Time Time Time 
Current
 Dload Upload Total Spent Left 
Speed
100 6781 0 6781 0 0 245k 0 --:--:-- --:--:-- --:--:-- 254k
[
 {
 "Created": 1482998541,
 "Id": 
"sha256:0c27604c726690da5f7368af31765903bbf196b8e5808c876a2abd25b681a17f",
 "Labels": null,
 "ParentId": "",
 "RepoDigests": null,
 "RepoTags": [
 "odoo:latest"
 ],
 "Size": 0,
 "VirtualSize": 0
 },
 {
 "Created": 1482966589,
 "Id": 
"sha256:411afb6272fbf5258c421ca5dd10bf212cddb40d78ac3962114b67bb78cc7c62",
"Labels": {},
 "ParentId": "",
 "RepoDigests": [
 
"docker.io/python@sha256:05d7f756d1980a83ca7419109334a6df47824e02eae93996c3d201
f96baf7cf3"
 ],
 "RepoTags": [
 "docker.io/python:latest"
 ],
 "Size": 687122335,
 "VirtualSize": 687122335
},
这里使用了/images/json 这个接入点，它将返回 Docker 守护进程中的所有镜
像的列表。
最后，也像命令行一样，也可以在 docker hub 上查找镜像。
# curl http://192.168.200.22:2375/images/search?term="jamtur01" | python 
-mjson.tool 
 % Total % Received % Xferd Average Speed Time Time 
Time Current
 Dload Upload Total Spent 
Left Speed
100 4387 0 4387 0 0 1023 0 --:--:-- 0:00:04 --:--:-- 
1023
[
 {
 "description": "",
 "index_name": "docker.io",
 "is_automated": true,
 "is_official": false,
 "is_trusted": true,
 "name": "jamtur01/docker-presentation",
 "registry_name": "docker.io",
 "star_count": 5
 },
 {
 "description": "",
 "index_name": "docker.io",
 "is_automated": false,
 "is_official": false,
 "is_trusted": false,
 "name": "jamtur01/dockerjenkins",
 "registry_name": "docker.io",
 "star_count": 3
 }

通过 API 管理 Docker 容器

Docker Remote API 同样也可以使用/container 参数列出所有正在的容器

# curl -s "http://127.0.0.1:2375/containers/json" | python -m json.tool 
[
 {
 "Command": "/entrypoint.sh /etc/docker/registry/config.yml",
 "Created": 1483003943,
 "HostConfig": {
 "NetworkMode": "default"
 },
 "Id":
 "09dda7fe410ba278db18ca1c0aade605083ac6151ce6e005527304f7cc3c5331",
 "Image": "docker.io/registry:latest",
 "ImageID": 
"sha256:c9bd19d022f6613fa0e3d73b2fe2b2cffe19ed629a426db9a652b597fccf07d4",
 "Labels": {},
 "Names": [
 "/registry"
 ],
 "NetworkSettings": {
 "Networks": {
 "bridge": {
 "Aliases": null,
 "EndpointID": 
"98594476f7c321b1301ea67aadbadbe412a6d44e49e3d6fb5ee152ba12eaab7f",
 "Gateway": "172.17.0.1",
 "GlobalIPv6Address": "",
 "GlobalIPv6PrefixLen": 0,
 "IPAMConfig": null,
 "IPAddress": "172.17.0.2",
 "IPPrefixLen": 16,
 "IPv6Gateway": "",
 "Links": null,
 "MacAddress": "02:42:ac:11:00:02",
 "NetworkID": ""
 }
 }
 },
 "Ports": [
 {
 "IP": "0.0.0.0",
 "PrivatePort": 5000,
 "PublicPort": 5000,
 "Type": "tcp"
 }
 ],
 "Status": "Up 53 minutes"
 } ]

使用 POST 请求来调用/containers/create 接入点来创建容器

# curl -X POST -H "Content-Type: application/json" 
http://127.0.0.1:2375/containers/create -d '{"image":"docker.io/python"}'
{"Id":"e7f1abb491ebfb1bb71b81ec9cb0eb5f72e7d4ce03bcaa5b491565c663ff1929",
"Warnings":null}