client: Pass an RPC Client to AllocRunners

As part of introducing support for CSI, AllocRunner hooks need to be
able to communicate with Nomad Servers for validation of and interaction
with storage volumes. Here we create a small RPCer interface and pass
the client (rpc client) to the AR in preparation for making these RPCs.

client/allocrunner/alloc_runner.go

@@ -158,6 +158,15 @@ type allocRunner struct {
 	serversContactedCh chan struct{}
 
 	taskHookCoordinator *taskHookCoordinator
+
+	// rpcClient is the RPC Client that should be used by the allocrunner and its
+	// hooks to communicate with Nomad Servers.
+	rpcClient RPCer
+}
+
+// RPCer is the interface needed by hooks to make RPC calls.
+type RPCer interface {
+	RPC(method string, args interface{}, reply interface{}) error
 }
 
 // NewAllocRunner returns a new allocation runner.
@@ -193,6 +202,7 @@ func NewAllocRunner(config *Config) (*allocRunner, error) {
 		devicemanager:            config.DeviceManager,
 		driverManager:            config.DriverManager,
 		serversContactedCh:       config.ServersContactedCh,
+		rpcClient:                config.RPCClient,
 	}
 
 	// Create the logger based on the allocation ID

client/allocrunner/alloc_runner_hooks.go

@@ -134,7 +134,7 @@ func (ar *allocRunner) initRunnerHooks(config *clientconfig.Config) error {
 			logger:         hookLogger,
 		}),
 		newConsulSockHook(hookLogger, alloc, ar.allocDir, config.ConsulConfig),
-		newCSIHook(hookLogger, alloc),
+		newCSIHook(hookLogger, alloc, ar.rpcClient),
 	}
 
 	return nil

client/allocrunner/config.go

@@ -68,4 +68,8 @@ type Config struct {
 	// ServersContactedCh is closed when the first GetClientAllocs call to
 	// servers succeeds and allocs are synced.
 	ServersContactedCh chan struct{}
+
+	// RPCClient is the RPC Client that should be used by the allocrunner and its
+	// hooks to communicate with Nomad Servers.
+	RPCClient RPCer
 }

client/allocrunner/csi_hook.go

@@ -10,8 +10,9 @@ import (
 //
 // It is a noop for allocs that do not depend on CSI Volumes.
 type csiHook struct {
-	alloc  *structs.Allocation
-	logger hclog.Logger
+	alloc     *structs.Allocation
+	logger    hclog.Logger
+	rpcClient RPCer
 }
 
 func (c *csiHook) Name() string {
@@ -27,10 +28,11 @@ func (c *csiHook) Prerun() error {
 	return nil
 }
 
-func newCSIHook(logger hclog.Logger, alloc *structs.Allocation) *csiHook {
+func newCSIHook(logger hclog.Logger, alloc *structs.Allocation, rpcClient RPCer) *csiHook {
 	return &csiHook{
-		alloc:  alloc,
-		logger: logger.Named("csi_hook"),
+		alloc:     alloc,
+		logger:    logger.Named("csi_hook"),
+		rpcClient: rpcClient,
 	}
 }
 

client/client.go

@@ -1088,6 +1088,7 @@ func (c *Client) restoreState() error {
 			DeviceManager:       c.devicemanager,
 			DriverManager:       c.drivermanager,
 			ServersContactedCh:  c.serversContactedCh,
+			RPCClient:           c,
 		}
 		c.configLock.RUnlock()
 
@@ -2351,6 +2352,7 @@ func (c *Client) addAlloc(alloc *structs.Allocation, migrateToken string) error
 		CSIManager:          c.csimanager,
 		DeviceManager:       c.devicemanager,
 		DriverManager:       c.drivermanager,
+		RPCClient:           c,
 	}
 	c.configLock.RUnlock()