istio sidecar自动注入过程分析

sidecar自动注入检查

istio通过机制实现sidecar的自动注入.istio sidecard在每个服务创建pod时都会被自动注入.

检查kube-apiserver

webhook支持需要kubernets1.9或者更高的版本,使用以下命令查看

[root@test1 ~]# kubectl api-versions | grep admissionregistration
admissionregistration.k8s.io/v1beta1

同时检查kube-apiserver有没按顺序加入参数mutatingadmissionwebhook和validatingadmissionwebhook

检查sidecar-injector的configmap

在sidecar-injector的configmap中设置policy=enabled字段来查看是否启用自动注入

[root@test1 ~]# kubectl describe cm istio-sidecar-injector -n istio-system
name:         istio-sidecar-injector
namespace:    istio-system
labels:       app=istio
              chart=istio-1.0.3
              heritage=tiller
              istio=sidecar-injector
              release=istio
...
data
====
config:
----
policy: enabled

检查namespace标签

为需要自动注入的namespace打上标签istio-injection: enabled

[root@test1 ~]# kubectl get namespace -l istio-injection
name           status    age       istio-injection
default        active    3d        enabled
istio-system   active    3d        
kube-public    active    3d        
kube-system    active    3d 

kubectl label namespace default istio-injection=enabled

sidecar自动注入过程

webhook过程

查看sidecar的webhook

[root@test1 ~]# kubectl get mutatingwebhookconfiguration -n istio-system
name                     created at
istio-sidecar-injector   2018-11-12t09:14:44z

[root@test1 ~]# kubectl describe mutatingwebhookconfiguration istio-sidecar-injector -n istio-system
name:         istio-sidecar-injector
namespace:    
labels:       app=istio-sidecar-injector
              chart=sidecarinjectorwebhook-1.0.3
              heritage=tiller
              release=istio
... ...
webhooks:
client config:
    ... ...
    service:
      name:        istio-sidecar-injector
      namespace:   istio-system
      path:        /inject
  failure policy:  fail
  name:            sidecar-injector.istio.io
  namespace selector:
    match labels:
      istio - injection:  enabled
  rules:
    api groups:
      
    api versions:
      v1
    operations:
      create
    resources:
      pods

由上面可以看出创建pod时会调用sidecar的webhook,接着向istio-sidecar-injector的服务发送inject注册(post https://istio-sidecar-injector.istio-system.svc:443/inject?timeout=30s).

查看istio-sidecar-injector的日志

[root@test-1 ~]# kubectl get pods -n istio-system | grep istio-sidecar
istio-sidecar-injector-d96cd9459-lbf66      1/1       running       0          13d

[root@test-1 ~]# kubectl logs istio-sidecar-injector-d96cd9459-lbf66 -n istio-system
2018-11-09t06:40:53.895979z info  admissionreview for kind=/v1, kind=pod namespace=default name= () uid=67d96021-e3ea-11e8-a721-00163e0c1d10 rfc6902patchoperation=create userinfo={system:unsecured  [system:masters system:authenticated] map[]}
2018-11-09t06:40:53.897821z info  admissionresponse: patch=[{"op":"add","path":"/spec/initcontainers","value":[{"name":"istio-init","image":"docker.io/istio/proxy_init:1.0.0","args":["-p","15001","-u","1337","-m","redirect","-i","10.0.0.1/24","-x","","-b","80,","-d",""] ... ...},{"op":"add","path":"/spec/containers/-","value":{"name":"istio-proxy","image":"docker.io/istio/proxyv2:1.0.0","args":["proxy","sidecar",... ...\"initcontainers\":[\"istio-init\"],\"containers\":[\"istio-proxy\"],\"volumes\":[\"istio-envoy\",\"istio-certs\"],\"imagepullsecrets\":null}"}}]

hook发送inject后,sidecar会返回两个container,istio-init和istio-proxy.下面我们来具体分析下.

获取pod具体信息

[root@test-1 ~]#kubectl describe pod nginx-dm-fff68d674-9tv9w 
name:           nginx-dm-fff68d674-9tv9w
namespace:      default
node:           10.0.3.126/10.0.3.126
start time:     fri, 09 nov 2018 14:40:53 +0800
labels:         name=nginx
                pod-template-hash=999248230
annotations:    sidecar.istio.io/status={"version":"5aa52d92ced8dab93e04a5a4701773b2f3d78968c04b05bb430f32e80a4d9be1","initcontainers":["istio-init"],"containers":["istio-proxy"],...
status:         running
ip:             172.30.2.21
controlled by:  replicaset/nginx-dm-fff68d674
init containers:
  istio-init:
    container id:  docker://43668b6cf4bb331542b8d98348a7670dad99b735aa0ef0ca572bf4ee1966538b
    image:         docker.io/istio/proxy_init:1.0.0
    image id:      docker-pullable://istio/proxy_init@sha256:345c40053b53b7cc70d12fb94379e5aa0befd979a99db80833cde671bd1f9fad
    port:          <none>
    host port:     <none>
    args:
      -p
      15001
      ... ...

containers:
  containers:
  nginx:
    container id:   docker://d917ffa9282bc4f82a0af1c8cbd6b51c0392fca6a85de6f8db6da128700db204
    image:          nginx:alpine
    image id:       
    port:           80/tcp
    host port:      0/tcp

  istio-proxy:
    container id:  docker://932a8bc6b85f1106cde057bd55598337bf7f9963fc4e796d3d88907d717a8eff
    image:         docker.io/istio/proxyv2:1.0.0
    image id:      docker-pullable://istio/proxyv2@sha256:77915a0b8c88cce11f04caf88c9ee30300d5ba1fe13146ad5ece9abf8826204c
    port:          <none>
    host port:     <none>
    args:
      proxy
      sidecar
      --configpath
      /etc/istio/proxy
      --binarypath
      /usr/local/bin/envoy
      --servicecluster
      ... ...

由具体信息可知,pod除了自身的容器外,还额外注入了两个容器.这就是由istio-sidecar-injector完成的.

proxy_init

proxy_init是一个init containers.init containers用于pod中执行初始化的任务,执行完毕退出后,才会执行后面的containers.

[root@test-1 ~]# docker inspect  docker.io/istio/proxy_init:1.0.0
[
    {
        "repotags": [
            "istio/proxy_init:1.0.0",
            "gcr.io/istio-release/proxy_init:1.0.0"
        ],
        "containerconfig": {
            ...
            "cmd": [
                "/bin/sh",
                "-c",
                "#(nop) ",
                "entrypoint [\"/usr/local/bin/istio-iptables.sh\"]"
            ],
            ...
        },
]

如上cmd可以知道,这个容器主要执行的是的脚本.

查看脚本内容

...
while getopts ":p:u:g:m:b:d:i:x:h" opt; do
  case ${opt} in
    p)
      proxy_port=${optarg}
      ;;
    u)
    ...

该脚本通过配置iptable来劫持pod中的流量.结合前面的-p 15001可知pod的数据流量被转发向envoy的15001端口.

proxyv2

查看pod内istio-proxy的进程

[root@test-1 ~]# kubectl exec nginx-dm-fff68d674-9tv9w -c istio-proxy -- ps -ef
uid        pid  ppid  c stime tty          time cmd
istio-p+     1     0  0 nov09 ?        00:00:12 /usr/local/bin/pilot-agent proxy sidecar --configpath /etc/istio/proxy --binarypath /usr/local/bin/envoy --servicecluster istio-proxy --drainduration 45s --parentshutdownduration 1m0s --discoveryaddress istio-pilot.istio-system:15007 --discoveryrefreshdelay 1s --zipkinaddress zipkin.istio-system:9411 --connecttimeout 10s --statsdudpaddress istio-statsd-prom-bridge.istio-system:9125 --proxyadminport 15000 --controlplaneauthpolicy none
istio-p+    24     1  0 nov09 ?        00:42:50 /usr/local/bin/envoy -c /etc/istio/proxy/envoy-rev0.json --restart-epoch 0 --drain-time-s 45 --parent-shutdown-time-s 60 --service-cluster istio-proxy --service-node sidecar~172.30.2.21~nginx-dm-fff68d674-9tv9w.default~default.svc.cluster.local --max-obj-name-len 189 -l warn --v2-config-only

上面有两个进程pilot-agent和envoy.
pilot-agent根据k8s api生成配置信息,并负责管理(启动,热更新,关闭等)整个envoy.生成的配置信息在 /etc/istio/proxy/envoy-rev0.json,具体内容可自己查看.

envoy由pilot-agent进程启动,envoy读取pilot-agent为它生成的配置文件(envoy-rev0.json),然后根据该文件的配置获取到pilot的地址,通过数据面标准api的xds接口从pilot拉取动态配置信息.

参考文档:
1.https://istio.io/docs/setup/kubernetes/sidecar-injection/
2.https://zhaohuabing.com/post/2018-09-25-istio-traffic-management-impl-intro/