Linux Capabilities Support in Mesos Containerizer

This document describes the linux/capabilities isolator. The isolator adds support for controlling Linux Capabilities of containers launched using the MesosContainerizer

The Linux capabilities isolator allows operators to control which privileged operations Mesos tasks may perform. Operators can specify which capabilities to allow for containers executing on an agent; containers on the other hand can expose which capabilities they need.

See the protobuf definition of CapabilityInfo::Capability for the list of currently exposed capabilities.

Agent setup

The Linux capabilities isolator is loaded when linux/capabilities is present in the agent's --isolation flag. Capabilities which should be allowed are passed with the --allowed_capabilities flag. This isolator requires the CAP_SETPCAP capability so agent processes typically need to be started as root. A possible agent startup invocation could be

sudo mesos-agent --master=<master ip> --ip=<agent ip>
  --isolation=linux/capabilities[,other isolation flags]

An empty list for --allowed_capabilities signifies that no capabilities are allowed, while an absent --allowed_capabilities flag signifies that all capabilities are allowed.

Task setup

In order for a Mesos task to acquire allowed capabilities it needs to declare required capabilities in the LinuxInfo of its ContainerInfo.

A Mesos task can only request capabilities which are allowed for the agent; a task requesting unallowed capabilities will be rejected.

If an empty list of capabilities is given the Mesos task will drop all capabilities; if the optional capability_info field is not set the container will be able to acquire the capabilities of the Mesos task's user.