一个容器多个进程，一个pod多个容器

1. 一个容器多个进程：在Docker的镜像编译脚本Dockerfile中带起多个进程，如下可以在contivNet.sh中启动多个进程

FROM 192.168.1.2:5001/world/centos7/ovs-2.6.4:1


COPY ./bin /contiv/bin/
COPY ./scripts /contiv/scripts/

ENTRYPOINT ["/contiv/scripts/contivNet.sh"]

2. 一个pod多个容器，可以在yaml文件中如下设置，在containers 中定义两个容器

# each master and worker node in a Kubernetes cluster.
kind: DaemonSet
apiVersion: extensions/v1beta1
metadata:
  name: contiv-netplugin-ovs
  namespace: kube-system
  labels:
    k8s-app: contiv-netplugin
spec:
  updateStrategy:
    type: OnDelete
  selector:
    matchLabels:
      k8s-app: contiv-netplugin
  template:
    metadata:
      labels:
        k8s-app: contiv-netplugin
      annotations:
        prometheus.io/scrape: 'true'
        prometheus.io/port: '9004'
        scheduler.alpha.kubernetes.io/critical-pod: ''
    spec:
      hostNetwork: true
      hostPID: true
      nodeSelector:
        node-role.kubernetes.io/node: ""
        node-network-driver: "ovs"
      tolerations:
      - key: node-role.kubernetes.io/master
        effect: NoSchedule
      serviceAccountName: contiv-netplugin
      containers:
        - name: netplugin-exporter
          image: 192.168.1.2:5001/contiv/exporter:0.1
          env:
            - name: CONTIV_ETCD
              valueFrom:
                configMapKeyRef:
                  name: contiv-config
                  key: contiv_etcd
            - name: CONTIV_ROLE
              value: 'ovs-netplugin'
          volumeMounts:
            - mountPath: /k8s_log/contiv
              name: var-log-contiv-exporter
              readOnly: false
        - name: contiv-netplugin
          image: 192.168.1.2:5001/contiv/netplugin:1.2.0_6.3
          env:
            - name: CONTIV_ROLE
              value: netplugin
            - name: CONTIV_NETPLUGIN_VLAN_UPLINKS
              value: enp130s0f0
            - name: CONTIV_NETPLUGIN_DRIVER
              value: ovs
            - name: CONTIV_NETPLUGIN_LOG_LEVEL
              value: INFO
            - name: CONTIV_NETPLUGIN_MODE
              valueFrom:
                configMapKeyRef:
                  name: contiv-config
                  key: contiv_mode
            - name: CONTIV_NETPLUGIN_VTEP_IP
              valueFrom:

可以在每个容器中启动一个进程，例如可以使用command启动进程：

 command:
 - /bin/sh
 - -c
 - /kubemark --morph=kubelet --name=$(NODE_NAME)  --kubeconfig=/kubeconfig/kubelet-$(NODE_NAME).kubeconfig $(CONTENT_TYPE) --alsologtostderr --v=4

这样一个pod中启动了两个容器，每个容器启动了一个进程。

一个pod多个容器实例： 打印log的辅助容器

当容器的log输出到文件时，我们想用kubectl logs来查看容器日志是查看不到的。我们可以使用启动另一个容器的方式来实现。例如，开源cillium的项目tetragon，每个Pod启动两个容器。一个是用于业务处理的tetragon容器，它运行的log写入日志/var/run/cilium/tetragon/tetragon.log, 另一个容器export-stdout是把日志内容输出到标准输出。这里贴出daemonset的部分定义文件：

    spec:
      containers:
      - args:
        - /var/run/cilium/tetragon/tetragon.log
        command:
        - hubble-export-stdout
        image: quay.io/cilium/hubble-export-stdout:v1.0.3
        imagePullPolicy: IfNotPresent
        name: export-stdout
        resources: {}
        securityContext: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        volumeMounts:
        - mountPath: /var/run/cilium/tetragon
          name: export-logs
      - args:
        - --config-dir=/etc/tetragon/tetragon.conf.d/
        env:
        - name: NODE_NAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: spec.nodeName
        image: quay.io/cilium/tetragon:v0.11.0
        imagePullPolicy: IfNotPresent
        livenessProbe:
          exec:
            command:
            - tetra
            - status
            - --server-address
            - localhost:54321
    ...

第一个容器export-stdout的参数是/var/run/cilium/tetragon/tetragon.log，运行的命令是hubble-export-stdout，而这个命令是一个简单的脚本，内容如下：

#!/bin/sh

set -e

tail -q -F "$@" 2> /dev/null

而制作这个容器镜像的dockerfile内容如下：

# skopeo inspect --override-os linux docker://busybox:1.36.0-musl  | jq -r .Digest
FROM docker.io/library/busybox:1.36.0-musl@sha256:b6252cc4d3a3a702284d828b89cf99d902fad4b00b4aebf2299aa15bfeae54bf as busybox

FROM scratch

# Use busybox statically compiled (musl) sh implementation
COPY --from=busybox /bin/sh /bin/sh
COPY --from=busybox /bin/tail /usr/bin/tail

COPY hubble-export-stdout /usr/local/bin/hubble-export-stdout
ENTRYPOINT ["/bin/sh", "/usr/local/bin/hubble-export-stdout"]