Add HashiCorp Nomad provider (#483)

* provider: adding Nomad provider

* updating CONTRIBUTING.md with Nomad provider

* updated README.md by adding the Nomad provider

* fix typo

* adding nomad/api and nomad/testutil deps

* adding Nomad binary dependency for provider tests

* fixed the nomad binary download command step and added tolerations to the nomad provider.

* adding nomad provider demo gif

* adding my name to authors

* adding two missing go-rootcerts files after dep ensure

* delete pod comment

vendor/github.com/hashicorp/raft/fsm.go

@@ -0,0 +1,136 @@
+package raft
+
+import (
+	"fmt"
+	"io"
+	"time"
+
+	"github.com/armon/go-metrics"
+)
+
+// FSM provides an interface that can be implemented by
+// clients to make use of the replicated log.
+type FSM interface {
+	// Apply log is invoked once a log entry is committed.
+	// It returns a value which will be made available in the
+	// ApplyFuture returned by Raft.Apply method if that
+	// method was called on the same Raft node as the FSM.
+	Apply(*Log) interface{}
+
+	// Snapshot is used to support log compaction. This call should
+	// return an FSMSnapshot which can be used to save a point-in-time
+	// snapshot of the FSM. Apply and Snapshot are not called in multiple
+	// threads, but Apply will be called concurrently with Persist. This means
+	// the FSM should be implemented in a fashion that allows for concurrent
+	// updates while a snapshot is happening.
+	Snapshot() (FSMSnapshot, error)
+
+	// Restore is used to restore an FSM from a snapshot. It is not called
+	// concurrently with any other command. The FSM must discard all previous
+	// state.
+	Restore(io.ReadCloser) error
+}
+
+// FSMSnapshot is returned by an FSM in response to a Snapshot
+// It must be safe to invoke FSMSnapshot methods with concurrent
+// calls to Apply.
+type FSMSnapshot interface {
+	// Persist should dump all necessary state to the WriteCloser 'sink',
+	// and call sink.Close() when finished or call sink.Cancel() on error.
+	Persist(sink SnapshotSink) error
+
+	// Release is invoked when we are finished with the snapshot.
+	Release()
+}
+
+// runFSM is a long running goroutine responsible for applying logs
+// to the FSM. This is done async of other logs since we don't want
+// the FSM to block our internal operations.
+func (r *Raft) runFSM() {
+	var lastIndex, lastTerm uint64
+
+	commit := func(req *commitTuple) {
+		// Apply the log if a command
+		var resp interface{}
+		if req.log.Type == LogCommand {
+			start := time.Now()
+			resp = r.fsm.Apply(req.log)
+			metrics.MeasureSince([]string{"raft", "fsm", "apply"}, start)
+		}
+
+		// Update the indexes
+		lastIndex = req.log.Index
+		lastTerm = req.log.Term
+
+		// Invoke the future if given
+		if req.future != nil {
+			req.future.response = resp
+			req.future.respond(nil)
+		}
+	}
+
+	restore := func(req *restoreFuture) {
+		// Open the snapshot
+		meta, source, err := r.snapshots.Open(req.ID)
+		if err != nil {
+			req.respond(fmt.Errorf("failed to open snapshot %v: %v", req.ID, err))
+			return
+		}
+
+		// Attempt to restore
+		start := time.Now()
+		if err := r.fsm.Restore(source); err != nil {
+			req.respond(fmt.Errorf("failed to restore snapshot %v: %v", req.ID, err))
+			source.Close()
+			return
+		}
+		source.Close()
+		metrics.MeasureSince([]string{"raft", "fsm", "restore"}, start)
+
+		// Update the last index and term
+		lastIndex = meta.Index
+		lastTerm = meta.Term
+		req.respond(nil)
+	}
+
+	snapshot := func(req *reqSnapshotFuture) {
+		// Is there something to snapshot?
+		if lastIndex == 0 {
+			req.respond(ErrNothingNewToSnapshot)
+			return
+		}
+
+		// Start a snapshot
+		start := time.Now()
+		snap, err := r.fsm.Snapshot()
+		metrics.MeasureSince([]string{"raft", "fsm", "snapshot"}, start)
+
+		// Respond to the request
+		req.index = lastIndex
+		req.term = lastTerm
+		req.snapshot = snap
+		req.respond(err)
+	}
+
+	for {
+		select {
+		case ptr := <-r.fsmMutateCh:
+			switch req := ptr.(type) {
+			case *commitTuple:
+				commit(req)
+
+			case *restoreFuture:
+				restore(req)
+
+			default:
+				panic(fmt.Errorf("bad type passed to fsmMutateCh: %#v", ptr))
+			}
+
+		case req := <-r.fsmSnapshotCh:
+			snapshot(req)
+
+		case <-r.shutdownCh:
+			return
+		}
+	}
+}