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Does Apache Mesos limits resources or isolates them?

In other words, Apache Mesos internal or docker resource isolation mechanism works?

If started app A requires 40% of CPU resources, and app B requires 61% - B app couldn't start, even if A app in practice loads CPU on 10%?

B app couldn't start, even if A app in practice loads CPU on 10%?

Yeah, because otherwise app A and app B would be both affected. Imagine A is using 40% of the cpu, app B, even declared it would like 61% cpu, can only use up to 60%. The reverse is also true (B using 61% and A can only get up to 39%).

So in general, no overbooking of resources. This is achieved in the resource allocation stage.

FYI how mesos launches tasks (tasks is the mesos terminology, instead of apps):

Launching tasks

In mesos, tasks are launched by frameworks.

Say you have a mesos slave with 1 cpus and 1GB RAM.

  • Mesos master would ask your framework: I offer you 1 cpu and 1GB ram, do you want to launch a task with it? In your case the framework would reply to the mesos master: "Yes, I want to launch a task A with 0.4cpus and 0.5GB ram, use this docker image and run this command ...".

Now there are 0.6 cpus left, but task B requires 0.61 cpu, so the framework can't launch the task B.

And don't confuse it with resource isolation, which is to guarantee the process of a task can't use more than it's allocated share of the cpu (and/or ram).

Resource isolation

Mesos imposes resource isolation by using cgroups. Mesos also supports launching tasks as docker containers, but the resource isolation of docker containers is also using cgroups.

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