Auxiliary plugin used mainly by other plugins to handle namespaces and microservices.
Agent has full support for Linux network namespaces. It is possible to attach
Linux interface/ARP/route into a new, existing or even yet-to-be-created network
namespace via the Namespace configuration section inside data model.
Namespace can be referenced in multiple ways. The most low-level link
to a namespace is a file descriptor associated with the symbolic link
automatically created in the proc filesystem, pointing to the definition
of the namespace used by a given process (/proc/<PID>/ns/net) or by a task
of a given process (/proc/<PID>/task/<TID>/ns/net).
A more common approach to reference namespace is to use just the PID
of the process whose namespace we want to attach to, or to create a bind-mount
of the symbolic link into /var/run/netns directory and use the filename of that
mount. The latter is called named namespace and it is created and managed for
example by the ip netns command line tool from the iproute2 package.
The advantage of named namespace is that it can outlive the process it was
originally created by.
namespace configuration section should be seen as a union of values. First,
set the type and then store the reference into the appropriate field (pid vs.
name vs microservice). Agent supports both PID-based references as well as
named namespaces.
Additionally, we provide a non-standard namespace reference, denoted
as MICROSERVICE_REF_NS, which is specific to ecosystems with microservices.
It is possible to attach interface/ARP/route into the namespace of a container
that runs microservice with a given label. To make it even simpler, it is not
required to start the microservice before the configured item is pushed.
The agent will postpone interface (re)configuration until the referenced
microservice gets launched. Behind the scenes, the agent communicates with
the docker daemon to construct and maintain an up-to-date map of microservice
labels to PIDs and IDs of their corresponding containers. Whenever a new
microservice is detected, all pending interfaces are moved to its namespace.