The rt_tables list is already in an ordered form in terms of priority.
Once one is found, it should be considered the optimal one and stop
looking for additional tables.
Not making direct exec calls to user binary interfaces has long been a
principle of kube-router. When kube-router was first coded, the netlink
library was missing significant features that forced us to exec out.
However, now netlink seems to have most of the functionality that we
need.
This converts all of the places where we can use netlink to use the
netlink functionality.
This prepares the way for broader refactors in the way that we handle
nodes by:
* Separating frequently used node logic from the controller creation
steps
* Keeping reused code DRY-er
* Adding interface abstractions for key groups of node data and starting
to rely on those more rather than concrete types
* Separating node data from the rest of the controller data structure so
that it smaller definitions of data can be passed around to functions
that need it rather than always passing the entire controller which
contains more data / surface area than most functions need.
Ever since version v6.5.0 of iproute2, iproute2 no longer automatically
creates the /etc/iproute2 files, instead preferring to add files to
/usr/lib/iproute2 and then later on /usr/share/iproute2.
This adds fallback path matching to kube-router so that it can find
/etc/iproute2/rt_tables wherever it is defined instead of just failing.
This also means people running kube-router in containers will need to
change their mounts depending on where this file is located on their
host OS. However, ensuring that this file is copied to `/etc/iproute2`
is a legitimate way to ensure that this is consistent across a fleet of
multiple OS versions.
