An initial, simple approach to this. The PeerMonitor will
check it's metrics, compare to the current set of peers and put
an alert in the alerts channel if the metrics for a peer have expired.
Cluster reads this channel looking for "ping" alerts. The leader
is in charge of triggering repins in all the Cids allocated to
a given peer.
Also, metrics are now broadcasted to the cluster instead of pushed only
to the leader. Since they happen every few seconds it should be okay
regarding how it scales. Main problem was that if the leader is the node
going down, the new leader will not now about it as it doesn't have any
metrics for it, so it won't trigger an alert. If it acted on that then
the component needs to know it is the leader, or cluster needs to
handle alerts in complicated ways when leadership changes. Detecting
leadership changes or letting a component know who is the leader is another
dependency from the consensus algorithm that should be avoided. Therefore
we broadcast, for the moment.
License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>
New PeerManager, Allocator, Informer components have been added along
with a new "replication_factor" configuration option.
First, cluster peers collect and push metrics (Informer) to the Cluster
leader regularly. The Informer is an interface that can be implemented
in custom wayts to support custom metrics.
Second, on a pin operation, using the information from the collected metrics,
an Allocator can provide a list of preferences as to where the new pin
should be assigned. The Allocator is an interface allowing to provide
different allocation strategies.
Both Allocator and Informer are Cluster Componenets, and have access
to the RPC API.
The allocations are kept in the shared state. Cluster peer failure
detection is still missing and re-allocation is still missing, although
re-pinning something when a node is down/metrics missing does re-allocate
the pin somewhere else.
License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>
