Dear group
In a project where performance is not an issue (yet, and possibly never), I
am thinking about the following cold-standy solution to enable us to
restart nodes without loosing state:
One node is running with Persistent Actors saving to a database. When that
node goes down, the other node is started manually, and reading all events
from the database it gets in the same state.
The problem with this is that we have to do something manually (start the
new server), and that we are unavailable in the meantime (for instance for
a GUI).
What is the next step, to have both nodes running at the same time, and not
appear down to the clients? Is it to have two (or more) nodes running in a
cluster, with all actors created as singletons?
We use a pattern where events we receive (over SOAP) are sent to a parent
actor, which forwards to children based on an ID in the event. If the ID is
unkown, the parent actor creates a new child.
The children builds up state based on the events, and publishes other
events based on this state. As I imagine it, the parent actor would be a
singleton, creating all the children on the same node... That way, starting
up the parent actor on an already running Akka instance would be pretty
fast, and reading from the same database it would get in the same state.
ClusterSingletonProxy
stashes away messages during this process, so we don't loose requests.
The doc, however, warns against the singleton pattern ("Using a singleton
should not be the first design choice"), and I am wondering what the
alternative is for my scenario.
Best regards,
Anders Båtstrand
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