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/state.go

@@ -0,0 +1,171 @@
+package raft
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+// RaftState captures the state of a Raft node: Follower, Candidate, Leader,
+// or Shutdown.
+type RaftState uint32
+
+const (
+	// Follower is the initial state of a Raft node.
+	Follower RaftState = iota
+
+	// Candidate is one of the valid states of a Raft node.
+	Candidate
+
+	// Leader is one of the valid states of a Raft node.
+	Leader
+
+	// Shutdown is the terminal state of a Raft node.
+	Shutdown
+)
+
+func (s RaftState) String() string {
+	switch s {
+	case Follower:
+		return "Follower"
+	case Candidate:
+		return "Candidate"
+	case Leader:
+		return "Leader"
+	case Shutdown:
+		return "Shutdown"
+	default:
+		return "Unknown"
+	}
+}
+
+// raftState is used to maintain various state variables
+// and provides an interface to set/get the variables in a
+// thread safe manner.
+type raftState struct {
+	// currentTerm commitIndex, lastApplied,  must be kept at the top of
+	// the struct so they're 64 bit aligned which is a requirement for
+	// atomic ops on 32 bit platforms.
+
+	// The current term, cache of StableStore
+	currentTerm uint64
+
+	// Highest committed log entry
+	commitIndex uint64
+
+	// Last applied log to the FSM
+	lastApplied uint64
+
+	// protects 4 next fields
+	lastLock sync.Mutex
+
+	// Cache the latest snapshot index/term
+	lastSnapshotIndex uint64
+	lastSnapshotTerm  uint64
+
+	// Cache the latest log from LogStore
+	lastLogIndex uint64
+	lastLogTerm  uint64
+
+	// Tracks running goroutines
+	routinesGroup sync.WaitGroup
+
+	// The current state
+	state RaftState
+}
+
+func (r *raftState) getState() RaftState {
+	stateAddr := (*uint32)(&r.state)
+	return RaftState(atomic.LoadUint32(stateAddr))
+}
+
+func (r *raftState) setState(s RaftState) {
+	stateAddr := (*uint32)(&r.state)
+	atomic.StoreUint32(stateAddr, uint32(s))
+}
+
+func (r *raftState) getCurrentTerm() uint64 {
+	return atomic.LoadUint64(&r.currentTerm)
+}
+
+func (r *raftState) setCurrentTerm(term uint64) {
+	atomic.StoreUint64(&r.currentTerm, term)
+}
+
+func (r *raftState) getLastLog() (index, term uint64) {
+	r.lastLock.Lock()
+	index = r.lastLogIndex
+	term = r.lastLogTerm
+	r.lastLock.Unlock()
+	return
+}
+
+func (r *raftState) setLastLog(index, term uint64) {
+	r.lastLock.Lock()
+	r.lastLogIndex = index
+	r.lastLogTerm = term
+	r.lastLock.Unlock()
+}
+
+func (r *raftState) getLastSnapshot() (index, term uint64) {
+	r.lastLock.Lock()
+	index = r.lastSnapshotIndex
+	term = r.lastSnapshotTerm
+	r.lastLock.Unlock()
+	return
+}
+
+func (r *raftState) setLastSnapshot(index, term uint64) {
+	r.lastLock.Lock()
+	r.lastSnapshotIndex = index
+	r.lastSnapshotTerm = term
+	r.lastLock.Unlock()
+}
+
+func (r *raftState) getCommitIndex() uint64 {
+	return atomic.LoadUint64(&r.commitIndex)
+}
+
+func (r *raftState) setCommitIndex(index uint64) {
+	atomic.StoreUint64(&r.commitIndex, index)
+}
+
+func (r *raftState) getLastApplied() uint64 {
+	return atomic.LoadUint64(&r.lastApplied)
+}
+
+func (r *raftState) setLastApplied(index uint64) {
+	atomic.StoreUint64(&r.lastApplied, index)
+}
+
+// Start a goroutine and properly handle the race between a routine
+// starting and incrementing, and exiting and decrementing.
+func (r *raftState) goFunc(f func()) {
+	r.routinesGroup.Add(1)
+	go func() {
+		defer r.routinesGroup.Done()
+		f()
+	}()
+}
+
+func (r *raftState) waitShutdown() {
+	r.routinesGroup.Wait()
+}
+
+// getLastIndex returns the last index in stable storage.
+// Either from the last log or from the last snapshot.
+func (r *raftState) getLastIndex() uint64 {
+	r.lastLock.Lock()
+	defer r.lastLock.Unlock()
+	return max(r.lastLogIndex, r.lastSnapshotIndex)
+}
+
+// getLastEntry returns the last index and term in stable storage.
+// Either from the last log or from the last snapshot.
+func (r *raftState) getLastEntry() (uint64, uint64) {
+	r.lastLock.Lock()
+	defer r.lastLock.Unlock()
+	if r.lastLogIndex >= r.lastSnapshotIndex {
+		return r.lastLogIndex, r.lastLogTerm
+	}
+	return r.lastSnapshotIndex, r.lastSnapshotTerm
+}