基于Kubernetes启动WebLogic后，发现JVM的最大heap size一直在700多M左右,通过
kubectl logs 察看pod启动状态,发现日志中并没有-Xms和-Xmx参数.日志部分如下:
[root@k8s-master fluentd-elasticsearch]# kubectl logs helloworld-service-4d72j..JAVA Memory arguments: -Djava.security.egd=file:/dev/./urandom.CLASSPATH=/u01/oracle/wlserver/../oracle_common/modules/javax.persistence_2.1.jar:/u01/oracle/wlserver/../wlserver/modules/com.oracle.weblogic.jpa21support_1.0.0.0_2-1.jar:/usr/java/jdk1.8.0_101/lib/tools.jar:/u01/oracle/wlserver/server/lib/weblogic_sp.jar:/u01/oracle/wlserver/server/lib/weblogic.jar:/u01/oracle/wlserver/../oracle_common/modules/net.sf.antcontrib_1.1.0.0_1-0b3/lib/ant-contrib.jar:/u01/oracle/wlserver/modules/features/oracle.wls.common.nodemanager_2.0.0.0.jar:/u01/oracle/wlserver/../oracle_common/modules/com.oracle.cie.config-wls-online_8.1.0.0.jar:/u01/oracle/wlserver/common/derby/lib/derbyclient.jar:/u01/oracle/wlserver/common/derby/lib/derby.jar:/u01/oracle/wlserver/server/lib/xqrl.jar.PATH=/u01/oracle/wlserver/server/bin:/u01/oracle/wlserver/../oracle_common/modules/org.apache.ant_1.9.2/bin:/usr/java/jdk1.8.0_101/jre/bin:/usr/java/jdk1.8.0_101/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/java/default/bin:/u01/oracle/oracle_common/common/bin:/u01/oracle/oracle_common/common/bin:/u01/oracle/wlserver/common/bin:/u01/oracle/user_projects/domains/base_domain/bin:/u01/oracle.**************************************************** To start WebLogic Server, use a username and ** password assigned to an admin-level user. For ** server administration, use the WebLogic Server ** console at http://hostname:port/console ****************************************************starting weblogic with Java version:java version "1.8.0_101"Java(TM) SE Runtime Environment (build 1.8.0_101-b13)Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)Starting WLS with line:/usr/java/jdk1.8.0_101/bin/java -server -Djava.security.egd=file:/dev/./urandom -Dweblogic.Name=AdminServer -Djava.security.policy=/u01/oracle/wlserver/server/lib/weblogic.policy -Dweblogic.ProductionModeEnabled=true -Djava.endorsed.dirs=/usr/java/jdk1.8.0_101/jre/lib/endorsed:/u01/oracle/wlserver/../oracle_common/modules/endorsed -da -Dwls.home=/u01/oracle/wlserver/server -Dweblogic.home=/u01/oracle/wlserver/server -Dweblogic.utils.cmm.lowertier.ServiceDisabled=true weblogic.Server
修改yaml文件中的limit参数,发现并不能影响JVM的size，开始怀疑JVM自己根据虚拟机以及启动的container实例的多少自动调整内存，调整replicationcontrol的数目，发现仍然每个进程JVM占用700m.
查阅相关材料，发现Linux Kernel cgroups针对JVM的内存控制机制如下:
- kubernetes switch(-limits)以及docker switch(-m, –memory and –memory-swap)设置都是为了让linux内核决定是否kill掉进程，如果他们消耗比较接近的话,但JVM不会意识到有这个限制。
- JVM的人体工程学机制(JVM ergonomic page)会优化成缺省占用1/4的物理内存，因为JVM并不意识到自己运行在container中，所以一个3G的虚拟机器，JVM最大占用的空间是3*1024/4=768M,正是我们在weblogic管理控制台上看到的jvm最大内存数.
- 如果我们采用limit或者-m 1G的参数，意味着Docker Daemon会限制1G的memory和1G的memory swap,也就是说你进程可以消耗接近2G的内存，不会被kill掉
如果我们想自己控制JVM所占用的heap size,我们可以通过在启动命令行中加入$JAVA_OPTIONS,比如:
$ docker run -d --name mycontainer8g -p 8080:8080 -m 800M -e JAVA_OPTIONS='-Xmx300m' rafabene/java-container:openjdk-env
如果是在kubernetes环境中，可以设置env环境变量把参数传入，因为setDomainEnv中，已经把JAVA_OPTIONS作为启动参数传入命令行。
示例如:
[root@k8s-master ~]# cat rc.yamlapiVersion: v1kind: ReplicationControllermetadata: name: helloworld-servicespec: replicas: 2 template: metadata: labels: weblogic-app: "helloworld" version: "0.1" spec: containers: - name: weblogichelloworld image: 1213-helloworld:v1 env: - name: "JAVA_OPTIONS" value: "-Xms1024m -Xmx1024m" ports: - containerPort: 7001---apiVersion: v1kind: Servicemetadata: name: helloworldsvc labels: weblogic-app: helloworldspec: type: NodePort ports: - port: 7001 protocol: TCP targetPort: 7001 name: http nodePort: 30001 selector: weblogic-app: helloworld
通过kubectl logs察看pods日志,可以看到-Xms和-Xmx已经被设置，
JAVA Memory arguments: -Djava.security.egd=file:/dev/./urandom.CLASSPATH=/u01/oracle/wlserver/../oracle_common/modules/javax.persistence_2.1.jar:/u01/oracle/wlserver/../wlserver/modules/com.oracle.weblogic.jpa21support_1.0.0.0_2-1.jar:/usr/java/jdk1.8.0_101/lib/tools.jar:/u01/oracle/wlserver/server/lib/weblogic_sp.jar:/u01/oracle/wlserver/server/lib/weblogic.jar:/u01/oracle/wlserver/../oracle_common/modules/net.sf.antcontrib_1.1.0.0_1-0b3/lib/ant-contrib.jar:/u01/oracle/wlserver/modules/features/oracle.wls.common.nodemanager_2.0.0.0.jar:/u01/oracle/wlserver/../oracle_common/modules/com.oracle.cie.config-wls-online_8.1.0.0.jar:/u01/oracle/wlserver/common/derby/lib/derbyclient.jar:/u01/oracle/wlserver/common/derby/lib/derby.jar:/u01/oracle/wlserver/server/lib/xqrl.jar.PATH=/u01/oracle/wlserver/server/bin:/u01/oracle/wlserver/../oracle_common/modules/org.apache.ant_1.9.2/bin:/usr/java/jdk1.8.0_101/jre/bin:/usr/java/jdk1.8.0_101/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/java/default/bin:/u01/oracle/oracle_common/common/bin:/u01/oracle/oracle_common/common/bin:/u01/oracle/wlserver/common/bin:/u01/oracle/user_projects/domains/base_domain/bin:/u01/oracle.**************************************************** To start WebLogic Server, use a username and ** password assigned to an admin-level user. For ** server administration, use the WebLogic Server ** console at http://hostname:port/console ****************************************************starting weblogic with Java version:java version "1.8.0_101"Java(TM) SE Runtime Environment (build 1.8.0_101-b13)Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)Starting WLS with line:/usr/java/jdk1.8.0_101/bin/java -server -Djava.security.egd=file:/dev/./urandom -Dweblogic.Name=AdminServer -Djava.security.policy=/u01/oracle/wlserver/server/lib/weblogic.policy -Dweblogic.ProductionModeEnabled=true -Xms1024m -Xmx1024m -Djava.endorsed.dirs=/usr/java/jdk1.8.0_101/jre/lib/endorsed:/u01/oracle/wlserver/../oracle_common/modules/endorsed -da -Dwls.home=/u01/oracle/wlserver/server -Dweblogic.home=/u01/oracle/wlserver/server -Dweblogic.utils.cmm.lowertier.ServiceDisabled=true weblogic.Server
转到WebLogic管理控制台去查看已经设置成功。
参考文档:
https://developers.redhat.com/blog/2017/03/14/java-inside-docker/
https://fabiokung.com/2014/03/13/memory-inside-linux-containers/