jepsen.nemesis.membership.state
This namespace defines the protocol for nemesis membership state machines—how to find the current view from a node, how to merge node views together, how to generate, apply, and complete operations, etc.
States should be Clojure defrecords, and have several special keys:
:node-views A map of nodes to the view of the cluster state from that particular node.
:view The merged view of the cluster state.
:pending A set of op op’ pairs we’ve applied to the cluster, but we’re not sure if they’re resolved yet.
All three of these keys will be initialized and merged into your State for you by the membership nemesis.
State
protocol
members
fs
(fs this)A set of all possible op :f’s we might generate.
invoke!
(invoke! this test op)Applies an operation we generated. Returns a completed op, or a tuple of op, state’.
merge-views
(merge-views this test)Derive a new :view from this state’s current :node-views. Used as our authoritative view of the cluster.
node-view
(node-view this test node)Returns the view of the cluster from a particular node. Return nil to indicate the view is currently unknown; the membership system will ignore nil results.
op
(op this test)Returns an operation we could perform next–or :pending if no operation is available.
resolve
(resolve this test)Called repeatedly on a state to evolve it towards some fixed new state. A more general form of resolve-op.
resolve-op
(resolve-op this test [op op'])Called with a particular pair of operations (both invocation and completion). If that operation has been resolved, returns a new version of the state. Otherwise, returns nil.
setup!
(setup! this test)Performs a one-time initialization of state. Should return a new state. This is a good place to open network connections or set up mutable resources.
teardown!
(teardown! this test)Called at the end of the test to dispose of this State. This is your opportunity to close network connections etc.