Resource Isolation

CGroup (abbreviated from control groups) is a Linux kernel feature to limit, account, and isolate resource usage (CPU, memory, disk I/O, etc.) of process groups.In Gearpump, we use cgroup to manage CPU resources.

Start CGroup Service

CGroup feature is only supported by Linux whose kernel version is larger than 2.6.18. Please also make sure the SELinux is disabled before start CGroup.

The following steps are supposed to be executed by root user.

Check /etc/cgconfig.conf exist or not. If not exists, please yum install libcgroup.
Run following command to see whether the cpu subsystem is already mounted to the file system.
```
lssubsys -m
```
Each subsystem in CGroup will have a corresponding mount file path in local file system. For example, the following output shows that cpu subsystem is mounted to file path /sys/fs/cgroup/cpu
```
cpu /sys/fs/cgroup/cpu
net_cls /sys/fs/cgroup/net_cls
blkio /sys/fs/cgroup/blkio
perf_event /sys/fs/cgroup/perf_event
```
If you want to assign permission to user gear to launch Gearpump Worker and applications with resource isolation enabled, you need to check gear's uid and gid in /etc/passwd file, let's take 500 for example.

Add following content to /etc/cgconfig.conf

# The mount point of cpu subsystem.
# If your system already mounted it, this segment should be eliminated.
mount {    
  cpu = /cgroup/cpu;
}

# Here the group name "gearpump" represents a node in CGroup's hierarchy tree.
# When the CGroup service is started, there will be a folder generated under the mount point of cpu subsystem,
# whose name is "gearpump".

group gearpump {
   perm {
       task {
           uid = 500;
           gid = 500;
        }
       admin {
           uid = 500;
           gid = 500;
       }
   }
   cpu {
   }
}

Please note that if the output of step 2 shows that cpu subsystem is already mounted, then the mount segment should not be included.

Then Start cgroup service
```
sudo service cgconfig restart
```
There should be a folder gearpump generated under the mount point of cpu subsystem and its owner is gear:gear.
Repeat the above-mentioned steps on each machine where you want to launch Gearpump.

Enable Cgroups in Gearpump

Login into the machine which has CGroup prepared with user gear.
```
ssh gear@node
```

Enter into Gearpump's home folder, edit gear.conf under folder ${GEARPUMP_HOME}/conf/

gearpump.worker.executor-process-launcher = "io.gearpump.cluster.worker.CGroupProcessLauncher"

gearpump.cgroup.root = "gearpump"

Please note the gearpump.cgroup.root gearpump must be consistent with the group name in /etc/cgconfig.conf.

Repeat the above-mentioned steps on each machine where you want to launch Gearpump
Start the Gearpump cluster, please refer to Deploy Gearpump in Standalone Mode

Launch Application From Command Line

Login into the machine which has Gearpump distribution.
Enter into Gearpump's home folder, edit gear.conf under folder ${GEARPUMP_HOME}/conf/
```
gearpump.cgroup.cpu-core-limit-per-executor = ${your_preferred_int_num}
```

Here the configuration is the number of CPU cores per executor can use and -1 means no limitation

Submit application

bin/gear app -jar examples/sol-2.12-0.9.0-assembly.jar -streamProducer 10 -streamProcessor 10

Then you can run command top to monitor the cpu usage.

Launch Application From Dashboard

If you want to submit the application from dashboard, by default the gearpump.cgroup.cpu-core-limit-per-executor is inherited from Worker's configuration. You can provide your own conf file to override it.

Limitations

Windows and Mac OS X don't support CGroup, so the resource isolation will not work even if you turn it on. There will not be any limitation for single executor's cpu usage.