When a locality is removed from EDS response, it's corresponding
sub-balancer will be removed from balancer group.
With this change, the sub-balancer won't be removed immediately. It will
be kept in a cache (for 15 minutes by default). If the locality is
re-added within the timeout, the sub-balancer in cache will be picked
and re-used.
This is a preparing change to support priority failover. It adds start() and close() to balancer group, so we can have a balancer group that's not in use, but has all the data and is ready to be started (think about a lower priority when the higher priority is in use).
A balancer group is split into two parts: static and dynamic:
static: the data from EDS, and gets updated even if balancer group is closed
balancer IDs and builders, addresses for each balancer
dynamic: the sub-balancers
These are only created when the balancer group is started. They are closed when the balancer group is closed.
And only when the balancer group is started, the sub-balancers will get address updates.
We will have a root level xds/ directory which will eventually contain
all xDS implementation including balancer, resolver, client etc.
The new structure looks something like this:
grpc/
|
+--xds/
|
+--internal/
| |
| +--balancer/
| |
| +--edsbalancer/
| |
| +--lrs/
| |
| +--orca/
|
+--experimental/
Users need to import grpc/xds/experimental package to get all xds
functionality, and this will eventually be moved to grpc/xds.
Also, moved grpc/balancer/internal/wrr to grpc/internal/wrr.
Doug Fawley