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3.4 Pod容器共享Volume
同一个Pod中的多个容器能够共享Pod级别的存储卷Volume。Volume可以被定义为各种类型，多个容器各自进行挂载操作，将一个Volume挂载为容器内部需要的目录，如图3.2所示。
图3.2 Pod中多个容器共享Volume
在下面的例子中，在Pod内包含两个容器：tomcat和busybox，在Pod级别设置Volume“app-logs”，用于tomcat向其中写日志文件，busybox读日志文件。
配置文件pod-volume-applogs.yaml的内容如下：
apiVersion: v1
kind: Pod
metadata:
name: volume-pod
spec:
containers:
- name: tomcat
image: tomcat
ports:
- containerPort: 8080
volumeMounts:
- name: app-logs
mountPath: /usr/local/tomcat/logs
- name: busybox
image: busybox
command: ["sh", "-c", "tail -f /logs/catalina*.log"]
volumeMounts:
- name: app-logs
mountPath: /logs
volumes:
- name: app-logs
emptyDir: {}
这里设置的Volume名为app-logs，类型为emptyDir（也可以设置为其他类型，详见第1章对Volume概念的说明），挂载到tomcat容器内的/usr/local/tomcat/logs目录，同时挂载到logreader容器内的/logs目录。tomcat容器在启动后会向/usr/local/tomcat/logs目录写文件，logreader容器就可以读取其中的文件了。
logreader容器的启动命令为tail -f /logs/catalina*.log，我们可以通过kubectl logs命令查看logreader容器的输出内容：
# kubectl logs volume-pod -c busybox
............
29-Jul-2016 12:55:59.626 INFO [localhost-startStop-1]
org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application
directory /usr/local/tomcat/webapps/manager
29-Jul-2016 12:55:59.722 INFO [localhost-startStop-1]
org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web
application directory /usr/local/tomcat/webapps/manager has finished in 96 ms
29-Jul-2016 12:55:59.740 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["http-apr-8080"]
29-Jul-2016 12:55:59.794 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["ajp-apr-8009"]
29-Jul-2016 12:56:00.604 INFO [main]
org.apache.catalina.startup.Catalina.start Server startup in 4052 ms
这个文件为tomcat生成的日志文件/usr/local/tomcat/logs/catalina.<date>.log的内容。登录tomcat容器进行查看：
# kubectl exec -ti volume-pod -c tomcat -- ls /usr/local/tomcat/logs
catalina.2016-07-29.log localhost_access_log.2016-07-29.txt
host-manager.2016-07-29.log manager.2016-07-29.log
# kubectl exec -ti volume-pod -c tomcat -- tail
/usr/local/tomcat/logs/catalina.2016-07-29.log
............
29-Jul-2016 12:55:59.722 INFO [localhost-startStop-1]
org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web
application directory /usr/local/tomcat/webapps/manager has finished in 96 ms
29-Jul-2016 12:55:59.740 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["http-apr-8080"]
29-Jul-2016 12:55:59.794 INFO [main] org.apache.coyote.AbstractProtocol.start
Starting ProtocolHandler ["ajp-apr-8009"]
29-Jul-2016 12:56:00.604 INFO [main]
org.apache.catalina.startup.Catalina.start Server startup in 4052 ms