解析 /var/run/docker.sock
2019-06-18 本文已影响0人
Lis_
image.png
docker.sock 是docker client 和docker daemon 在localhost进行通信的socket文件。
今天我们直接call这个socket文件来创建容器，启动容器。（其实就是直接call docker daemon API而不是通过docker client的方式去操控docker daemon）。
什么是unix socket？
unix socket可以让一个程序通过类似处理一个文件的方式和另一个程序通信，这是一种进程间通信的方式（IPC）。
当你在host上安装并且启动好docker，docker daemon 会自动创建一个socket文件并且保存在/var/run/docker.sock目录下。docker daemon监听着socket中即将到来的链接请求（可以通过-H unix:///var/run/docker.sock设定docker daemon监听的socket文件，-H参数还可以设定监听tcp:port或者其它的unix socket），当一个链接请求到来时，它会使用标准IO来读写数据。
创建容器
# curl -XPOST --unix-socket /var/run/docker.sock -d '{"Image":"nginx"}' -H 'Content-Type: application/json' http://localhost/containers/create
{"Id":"a4bc1943984d7fccd902ac9a5f5966b72b438a2f4f5764f319e181b601dbc886","Warnings":null}
# curl -XPOST --unix-socket /var/run/docker.sock http://localhost/containers/a4bc1943984d7fccd902ac9a5f5966b72b438a2f4f5764f319e181b601dbc886/start
# docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a4bc1943984d nginx "nginx -g 'daemon of…" 2 minutes ago Up 22 seconds 80/tcp zealous_buck
docker API 还暴露出event接口来记录操作API的事件
curl --unix-socket /var/run/docker.sock http://localhost/events
当用docker client 进行操作时，会看到打印出来的event
docker run -it --rm nginx sh
# curl --unix-socket /var/run/docker.sock http://localhost/events
{"status":"create","id":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","from":"nginx","Type":"container","Action":"create","Actor":{"ID":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"ecstatic_mendeleev"}},"scope":"local","time":1560835913,"timeNano":1560835913703025294}
{"status":"attach","id":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","from":"nginx","Type":"container","Action":"attach","Actor":{"ID":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"ecstatic_mendeleev"}},"scope":"local","time":1560835913,"timeNano":1560835913704314497}
{"Type":"network","Action":"connect","Actor":{"ID":"b049de6ba0d38d1af9d93487b60ed861a08e65ecf3a644b0e6745fa903eb3d06","Attributes":{"container":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","name":"bridge","type":"bridge"}},"scope":"local","time":1560835913,"timeNano":1560835913730994076}
{"status":"start","id":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","from":"nginx","Type":"container","Action":"start","Actor":{"ID":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"ecstatic_mendeleev"}},"scope":"local","time":1560835914,"timeNano":1560835914138532930}
{"status":"resize","id":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","from":"nginx","Type":"container","Action":"resize","Actor":{"ID":"94e4de2eed35056c5434c84e544bc429b84cfbf4f99b458464eb87f3394eaead","Attributes":{"height":"49","image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"ecstatic_mendeleev","width":"136"}},"scope":"local","time":1560835914,"timeNano":1560835914140380103}
还可以通过将bind mounting方式使用docker.socket
# docker run -it -v /var/run/docker.sock:/var/run/docker.sock busybox sh
apk update
apk add curl
/ # curl --unix-socket /var/run/docker.sock http://localhost/events
# docker run -it --rm nginx sh
/ # curl --unix-socket /var/run/docker.sock http://localhost/events
{"status":"create","id":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","from":"nginx","Type":"container","Action":"create","Actor":{"ID":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"gracious_hopper"}},"scope":"local","time":1560836531,"timeNano":1560836531969907371}
{"status":"attach","id":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","from":"nginx","Type":"container","Action":"attach","Actor":{"ID":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"gracious_hopper"}},"scope":"local","time":1560836531,"timeNano":1560836531971179743}
{"Type":"network","Action":"connect","Actor":{"ID":"b049de6ba0d38d1af9d93487b60ed861a08e65ecf3a644b0e6745fa903eb3d06","Attributes":{"container":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","name":"bridge","type":"bridge"}},"scope":"local","time":1560836532,"timeNano":1560836532003253979}
{"status":"start","id":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","from":"nginx","Type":"container","Action":"start","Actor":{"ID":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","Attributes":{"image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"gracious_hopper"}},"scope":"local","time":1560836532,"timeNano":1560836532459395027}
{"status":"resize","id":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","from":"nginx","Type":"container","Action":"resize","Actor":{"ID":"af36698121cb5b0734d3aa746c3f9519f54bb9bb63ae23a16bf3188a9fd7c724","Attributes":{"height":"47","image":"nginx","maintainer":"NGINX Docker Maintainers \u003cdocker-maint@nginx.com\u003e","name":"gracious_hopper","width":"88"}},"scope":"local","time":1560836532,"timeNano":1560836532461732028}
通过bind mounting的方式可以在容器中控制docker daemon.
分析docker
以docker 18.09.6 为例，分析一下docker，在docker 安装后，有docker``dockerd``docker-init``docker-proxy``runc这个几个二进制文件。
docker是docker client，dockerd是docker daemon，docker daemon调用runc最终创建container。
以docker 18.09.6为例，在x86_64 redhat 7.5环境中，通过rpm包安装docker，需要安装以下几个包
docker-ce-18.09.6-3.el7.x86_64.rpm``docker-ce-cli-18.09.6-3.el7.x86_64.rpm``containerd.io-1.2.5-3.1.el7.x86_64.rpm
我们来看看这些包中都包含了哪些内容
docker-ce 包含了主要的docker 包
# rpm -qpl docker-ce-18.09.6-3.el7.x86_64.rpm
warning: docker-ce-18.09.6-3.el7.x86_64.rpm: Header V4 RSA/SHA512 Signature, key ID 621e9f35: NOKEY
/usr/bin/docker-init
/usr/bin/docker-proxy
/usr/bin/dockerd-ce
/usr/lib/systemd/system/docker.service
/usr/lib/systemd/system/docker.socket
/var/lib/docker-engine/distribution_based_engine-ce.json
docker-ce-cli包含了docker client和一些帮助文档
# rpm -qpl docker-ce-cli-18.09.6-3.el7.x86_64.rpm
warning: docker-ce-cli-18.09.6-3.el7.x86_64.rpm: Header V4 RSA/SHA512 Signature, key ID 621e9f35: NOKEY
/usr/bin/docker
/usr/share/bash-completion/completions/docker
/usr/share/doc/docker-ce-cli-18.09.6
/usr/share/doc/docker-ce-cli-18.09.6/LICENSE
/usr/share/doc/docker-ce-cli-18.09.6/MAINTAINERS
/usr/share/doc/docker-ce-cli-18.09.6/NOTICE
/usr/share/doc/docker-ce-cli-18.09.6/README.md
/usr/share/fish/vendor_completions.d/docker.fish
/usr/share/man/man1/docker-attach.1.gz
......
containerd中包含了containerd containerd-shim ctr runc
# rpm -qpl containerd.io-1.2.5-3.1.el7.x86_64.rpm
warning: containerd.io-1.2.5-3.1.el7.x86_64.rpm: Header V4 RSA/SHA512 Signature, key ID 621e9f35: NOKEY
/etc/containerd
/etc/containerd/config.toml
/usr/bin/containerd
/usr/bin/containerd-shim
/usr/bin/ctr
/usr/lib/systemd/system/containerd.service
/usr/sbin/runc
/usr/share/doc/containerd.io-1.2.5
/usr/share/doc/containerd.io-1.2.5/README.md
/usr/share/licenses/containerd.io-1.2.5
/usr/share/licenses/containerd.io-1.2.5/LICENSE
/usr/share/man/man1/containerd-config.1
/usr/share/man/man1/containerd.1
/usr/share/man/man1/ctr.1
/usr/share/man/man5/containerd-config.toml.5
