core/internal/consensus/consensus.go - monogon - Gitiles

 // Copyright 2020 The Monogon Project Authors.
 //
 // SPDX-License-Identifier: Apache-2.0
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 // package consensus manages the embedded etcd cluster.
 package consensus

 import (
 	"bytes"
 	"context"
 	"crypto/x509"
 	"encoding/hex"
 	"encoding/pem"
 	"fmt"
 	"io/ioutil"
 	"math/rand"
 	"net/url"
 	"os"
 	"path"
 	"path/filepath"
 	"strings"
 	"time"

 	"git.monogon.dev/source/nexantic.git/core/internal/common"
 	"git.monogon.dev/source/nexantic.git/core/internal/common/service"

 	"git.monogon.dev/source/nexantic.git/core/generated/api"

 	"git.monogon.dev/source/nexantic.git/core/internal/consensus/ca"
 	"github.com/pkg/errors"
 	"go.etcd.io/etcd/clientv3"
 	"go.etcd.io/etcd/clientv3/namespace"
 	"go.etcd.io/etcd/embed"
 	"go.etcd.io/etcd/etcdserver/api/membership"
 	"go.etcd.io/etcd/pkg/types"
 	"go.etcd.io/etcd/proxy/grpcproxy/adapter"
 	"go.uber.org/zap"
 	"golang.org/x/sys/unix"
 )

 const (
 	DefaultClusterToken = "SIGNOS"
 	DefaultLogger       = "zap"
 )

 const (
 	CAPath      = "ca.pem"
 	CertPath    = "cert.pem"
 	KeyPath     = "cert-key.pem"
 	CRLPath     = "ca-crl.der"
 	CRLSwapPath = "ca-crl.der.swp"
 )

 const (
 	LocalListenerURL = "unix:///consensus/listener.sock:0"
 )

 type (
 	Service struct {
 		*service.BaseService

 		etcd  *embed.Etcd
 		kv    clientv3.KV
 		ready bool

 		// bootstrapCA and bootstrapCert cache the etcd cluster CA data during bootstrap.
 		bootstrapCA   *ca.CA
 		bootstrapCert []byte

 		watchCRLTicker *time.Ticker
 		lastCRL        []byte

 		config *Config
 	}

 	Config struct {
 		Name           string
 		DataDir        string
 		InitialCluster string
 		NewCluster     bool
 		ExternalHost   string
 		ListenHost     string
 	}

 	Member struct {
 		ID      uint64
 		Name    string
 		Address string
 		Synced  bool
 	}
 )

 func NewConsensusService(config Config, logger *zap.Logger) (*Service, error) {
 	consensusServer := &Service{
 		config: &config,
 	}
 	consensusServer.BaseService = service.NewBaseService("consensus", logger, consensusServer)

 	return consensusServer, nil
 }

 func (s *Service) OnStart() error {
 	// See: https://godoc.org/github.com/coreos/etcd/embed#Config

 	if s.config == nil {
 		return errors.New("config for consensus is nil")
 	}

 	cfg := embed.NewConfig()

 	cfg.PeerTLSInfo.CertFile = filepath.Join(s.config.DataDir, CertPath)
 	cfg.PeerTLSInfo.KeyFile = filepath.Join(s.config.DataDir, KeyPath)
 	cfg.PeerTLSInfo.TrustedCAFile = filepath.Join(s.config.DataDir, CAPath)
 	cfg.PeerTLSInfo.ClientCertAuth = true
 	cfg.PeerTLSInfo.CRLFile = filepath.Join(s.config.DataDir, CRLPath)

 	lastCRL, err := ioutil.ReadFile(cfg.PeerTLSInfo.CRLFile)
 	if err != nil {
 		return fmt.Errorf("failed to read etcd CRL: %w", err)
 	}
 	s.lastCRL = lastCRL

 	// Expose etcd to local processes
 	if err := os.MkdirAll("/consensus", 0700); err != nil {
 		return fmt.Errorf("Failed to create consensus runtime state directory: %w", err)
 	}
 	listenerURL, err := url.Parse(LocalListenerURL)
 	if err != nil {
 		panic(err)
 	}
 	cfg.LCUrls = []url.URL{*listenerURL}

 	// Advertise Peer URLs
 	apURL, err := url.Parse(fmt.Sprintf("https://%s:%d", s.config.ExternalHost, common.ConsensusPort))
 	if err != nil {
 		return fmt.Errorf("invalid external_host or listen_port: %w", err)
 	}

 	// Listen Peer URLs
 	lpURL, err := url.Parse(fmt.Sprintf("https://%s:%d", s.config.ListenHost, common.ConsensusPort))
 	if err != nil {
 		return fmt.Errorf("invalid listen_host or listen_port: %w", err)
 	}
 	cfg.APUrls = []url.URL{*apURL}
 	cfg.LPUrls = []url.URL{*lpURL}
 	cfg.ACUrls = []url.URL{}

 	cfg.Dir = s.config.DataDir
 	cfg.InitialClusterToken = DefaultClusterToken
 	cfg.Name = s.config.Name

 	// Only relevant if creating or joining a cluster; otherwise settings will be ignored
 	if s.config.NewCluster {
 		cfg.ClusterState = "new"
 		cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
 	} else if s.config.InitialCluster != "" {
 		cfg.ClusterState = "existing"
 		cfg.InitialCluster = s.config.InitialCluster
 	}

 	cfg.Logger = DefaultLogger

 	server, err := embed.StartEtcd(cfg)
 	if err != nil {
 		return err
 	}
 	s.etcd = server

 	// Override the logger
 	//*server.GetLogger() = *s.Logger.With(zap.String("component", "etcd"))
 	// TODO(leo): can we uncomment this?

 	go func() {
 		s.Logger.Info("waiting for etcd to become ready")
 		<-s.etcd.Server.ReadyNotify()
 		s.Logger.Info("etcd is now ready")
 	}()

 	// Inject kv client
 	s.kv = clientv3.NewKVFromKVClient(adapter.KvServerToKvClient(s.etcd.Server), nil)

 	// Start CRL watcher
 	go s.watchCRL()

 	return nil
 }

 // WriteCertificateFiles writes the given node certificate data to local storage
 // such that it can be used by the embedded etcd server.
 // Unfortunately, we cannot pass the certificates directly to etcd.
 func (s *Service) WriteCertificateFiles(certs *api.ConsensusCertificates) error {
 	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CRLPath), certs.Crl, 0600); err != nil {
 		return err
 	}
 	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CertPath),
 		pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certs.Cert}), 0600); err != nil {
 		return err
 	}
 	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, KeyPath),
 		pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: certs.Key}), 0600); err != nil {
 		return err
 	}
 	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CAPath),
 		pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certs.Ca}), 0600); err != nil {
 		return err
 	}
 	return nil
 }

 // PrecreateCA generates the etcd cluster certificate authority and writes it to local storage.
 func (s *Service) PrecreateCA() error {
 	// Provision an etcd CA
 	etcdRootCA, err := ca.New("Smalltown etcd Root CA")
 	if err != nil {
 		return err
 	}
 	cert, privkey, err := etcdRootCA.IssueCertificate(s.config.ExternalHost)
 	if err != nil {
 		return fmt.Errorf("failed to self-issue a certificate: %w", err)
 	}
 	if err := os.MkdirAll(s.config.DataDir, 0700); err != nil {
 		return fmt.Errorf("failed to create consensus data dir: %w", err)
 	}
 	// Preserve certificate for later injection
 	s.bootstrapCert = cert
 	if err := s.WriteCertificateFiles(&api.ConsensusCertificates{
 		Ca:   etcdRootCA.CACertRaw,
 		Crl:  etcdRootCA.CRLRaw,
 		Cert: cert,
 		Key:  privkey,
 	}); err != nil {
 		return fmt.Errorf("failed to setup certificates: %w", err)
 	}
 	s.bootstrapCA = etcdRootCA
 	return nil
 }

 const (
 	caPathEtcd    = "/etcd-ca/ca.der"
 	caKeyPathEtcd = "/etcd-ca/ca-key.der"
 	crlPathEtcd   = "/etcd-ca/crl.der"

 	// This prefix stores the individual certs the etcd CA has issued.
 	certPrefixEtcd = "/etcd-ca/certs"
 )

 // InjectCA copies the CA from data cached during PrecreateCA to etcd.
 // Requires a previous call to PrecreateCA.
 func (s *Service) InjectCA() error {
 	if s.bootstrapCA == nil || s.bootstrapCert == nil {
 		panic("bootstrapCA or bootstrapCert are nil - missing PrecreateCA call?")
 	}
 	if _, err := s.kv.Put(context.Background(), caPathEtcd, string(s.bootstrapCA.CACertRaw)); err != nil {
 		return err
 	}
 	// TODO(lorenz): Should be wrapped by the master key
 	if _, err := s.kv.Put(context.Background(), caKeyPathEtcd, string([]byte(*s.bootstrapCA.PrivateKey))); err != nil {
 		return err
 	}
 	if _, err := s.kv.Put(context.Background(), crlPathEtcd, string(s.bootstrapCA.CRLRaw)); err != nil {
 		return err
 	}
 	certVal, err := x509.ParseCertificate(s.bootstrapCert)
 	if err != nil {
 		return err
 	}
 	serial := hex.EncodeToString(certVal.SerialNumber.Bytes())
 	if _, err := s.kv.Put(context.Background(), path.Join(certPrefixEtcd, serial), string(s.bootstrapCert)); err != nil {
 		return fmt.Errorf("failed to persist certificate: %w", err)
 	}
 	// Clear out bootstrap CA after injecting
 	s.bootstrapCA = nil
 	s.bootstrapCert = []byte{}
 	return nil
 }

 func (s *Service) etcdGetSingle(path string) ([]byte, int64, error) {
 	res, err := s.kv.Get(context.Background(), path)
 	if err != nil {
 		return nil, -1, fmt.Errorf("failed to get key from etcd: %w", err)
 	}
 	if len(res.Kvs) != 1 {
 		return nil, -1, errors.New("key not available or multiple keys returned")
 	}
 	return res.Kvs[0].Value, res.Kvs[0].ModRevision, nil
 }

 func (s *Service) getCAFromEtcd() (*ca.CA, int64, error) {
 	// TODO: Technically this could be done in a single request, but it's more logic
 	caCert, _, err := s.etcdGetSingle(caPathEtcd)
 	if err != nil {
 		return nil, -1, fmt.Errorf("failed to get CA certificate from etcd: %w", err)
 	}
 	caKey, _, err := s.etcdGetSingle(caKeyPathEtcd)
 	if err != nil {
 		return nil, -1, fmt.Errorf("failed to get CA key from etcd: %w", err)
 	}
 	// TODO: Unwrap CA key once wrapping is implemented
 	crl, crlRevision, err := s.etcdGetSingle(crlPathEtcd)
 	if err != nil {
 		return nil, -1, fmt.Errorf("failed to get CRL from etcd: %w", err)
 	}
 	idCA, err := ca.FromCertificates(caCert, caKey, crl)
 	if err != nil {
 		return nil, -1, fmt.Errorf("failed to take CA online: %w", err)
 	}
 	return idCA, crlRevision, nil
 }

 func (s *Service) IssueCertificate(hostname string) (*api.ConsensusCertificates, error) {
 	idCA, _, err := s.getCAFromEtcd()
 	if err != nil {
 		return nil, err
 	}
 	cert, key, err := idCA.IssueCertificate(hostname)
 	if err != nil {
 		return nil, fmt.Errorf("failed to issue certificate: %w", err)
 	}
 	certVal, err := x509.ParseCertificate(cert)
 	if err != nil {
 		return nil, err
 	}
 	serial := hex.EncodeToString(certVal.SerialNumber.Bytes())
 	if _, err := s.kv.Put(context.Background(), path.Join(certPrefixEtcd, serial), string(cert)); err != nil {
 		// We issued a certificate, but failed to persist it. Return an error and forget it ever happened.
 		return nil, fmt.Errorf("failed to persist certificate: %w", err)
 	}
 	return &api.ConsensusCertificates{
 		Ca:   idCA.CACertRaw,
 		Cert: cert,
 		Crl:  idCA.CRLRaw,
 		Key:  key,
 	}, nil
 }

 func (s *Service) RevokeCertificate(hostname string) error {
 	rand.Seed(time.Now().UnixNano())
 	for {
 		idCA, crlRevision, err := s.getCAFromEtcd()
 		if err != nil {
 			return err
 		}
 		allIssuedCerts, err := s.kv.Get(context.Background(), certPrefixEtcd, clientv3.WithPrefix())
 		for _, cert := range allIssuedCerts.Kvs {
 			certVal, err := x509.ParseCertificate(cert.Value)
 			if err != nil {
 				s.Logger.Error("Failed to parse previously issued certificate, this is a security risk", zap.Error(err))
 				continue
 			}
 			for _, dnsName := range certVal.DNSNames {
 				if dnsName == hostname {
 					// Revoke this
 					if err := idCA.Revoke(certVal.SerialNumber); err != nil {
 						// We need to fail if any single revocation fails otherwise outer applications
 						// have no chance of calling this safely
 						return err
 					}
 				}
 			}
 		}
 		// TODO(leo): this needs a test
 		cmp := clientv3.Compare(clientv3.ModRevision(crlPathEtcd), "=", crlRevision)
 		op := clientv3.OpPut(crlPathEtcd, string(idCA.CRLRaw))
 		res, err := s.kv.Txn(context.Background()).If(cmp).Then(op).Commit()
 		if err != nil {
 			return fmt.Errorf("failed to persist new CRL in etcd: %w", err)
 		}
 		if res.Succeeded { // Transaction has succeeded
 			break
 		}
 		// Sleep a random duration between 0 and 300ms to reduce serialization failures
 		time.Sleep(time.Duration(rand.Intn(300)) * time.Millisecond)
 	}
 	return nil
 }

 func (s *Service) watchCRL() {
 	// TODO(lorenz): Change etcd client to WatchableKV and make this an actual watch
 	// This needs changes in more places, so leaving it now
 	s.watchCRLTicker = time.NewTicker(30 * time.Second)
 	for range s.watchCRLTicker.C {
 		crl, _, err := s.etcdGetSingle(crlPathEtcd)
 		if err != nil {
 			s.Logger.Warn("Failed to check for new CRL", zap.Error(err))
 			continue
 		}
 		// This is cryptographic material but not secret, so no constant time compare necessary here
 		if !bytes.Equal(crl, s.lastCRL) {
 			if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CRLSwapPath), crl, 0600); err != nil {
 				s.Logger.Warn("Failed to write updated CRL", zap.Error(err))
 			}
 			// This uses unix.Rename to guarantee a particular atomic update behavior
 			if err := unix.Rename(filepath.Join(s.config.DataDir, CRLSwapPath), filepath.Join(s.config.DataDir, CRLPath)); err != nil {
 				s.Logger.Warn("Failed to atomically swap updated CRL", zap.Error(err))
 			}
 		}
 	}
 }

 func (s *Service) OnStop() error {
 	s.watchCRLTicker.Stop()
 	s.etcd.Close()

 	return nil
 }

 // IsProvisioned returns whether the node has been setup before and etcd has a data directory
 func (s *Service) IsProvisioned() bool {
 	_, err := os.Stat(s.config.DataDir)

 	return !os.IsNotExist(err)
 }

 // IsReady returns whether etcd is ready and synced
 func (s *Service) IsReady() bool {
 	return s.ready
 }

 // AddMember adds a new etcd member to the cluster
 func (s *Service) AddMember(ctx context.Context, name string, url string) (uint64, error) {
 	urls, err := types.NewURLs([]string{url})
 	if err != nil {
 		return 0, err
 	}

 	member := membership.NewMember(name, urls, DefaultClusterToken, nil)

 	_, err = s.etcd.Server.AddMember(ctx, *member)
 	if err != nil {
 		return 0, err
 	}

 	return uint64(member.ID), nil
 }

 // RemoveMember removes a member from the etcd cluster
 func (s *Service) RemoveMember(ctx context.Context, id uint64) error {
 	_, err := s.etcd.Server.RemoveMember(ctx, id)
 	return err
 }

 // Health returns the current cluster health
 func (s *Service) Health() {
 }

 // GetConfig returns the current consensus config
 func (s *Service) GetConfig() Config {
 	return *s.config
 }

 // SetConfig sets the consensus config. Changes are only applied when the service is restarted.
 func (s *Service) SetConfig(config Config) {
 	s.config = &config
 }

 // GetInitialClusterString returns the InitialCluster string that can be used to bootstrap a consensus node
 func (s *Service) GetInitialClusterString() string {
 	members := s.etcd.Server.Cluster().Members()
 	clusterString := strings.Builder{}

 	for i, m := range members {
 		if i != 0 {
 			clusterString.WriteString(",")
 		}
 		clusterString.WriteString(m.Name)
 		clusterString.WriteString("=")
 		clusterString.WriteString(m.PickPeerURL())
 	}

 	return clusterString.String()
 }

 // GetNodes returns a list of consensus nodes
 func (s *Service) GetNodes() []Member {
 	members := s.etcd.Server.Cluster().Members()
 	cMembers := make([]Member, len(members))
 	for i, m := range members {
 		cMembers[i] = Member{
 			ID:      uint64(m.ID),
 			Name:    m.Name,
 			Address: m.PickPeerURL(),
 			Synced:  !m.IsLearner,
 		}
 	}

 	return cMembers
 }

 func (s *Service) GetStore(module, space string) clientv3.KV {
 	return namespace.NewKV(s.kv, fmt.Sprintf("%s:%s", module, space))
 }
	// Copyright 2020 The Monogon Project Authors.
	//
	// SPDX-License-Identifier: Apache-2.0
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	// package consensus manages the embedded etcd cluster.
	package consensus

	import (
	"bytes"
	"context"
	"crypto/x509"
	"encoding/hex"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"math/rand"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strings"
	"time"

	"git.monogon.dev/source/nexantic.git/core/internal/common"
	"git.monogon.dev/source/nexantic.git/core/internal/common/service"

	"git.monogon.dev/source/nexantic.git/core/generated/api"

	"git.monogon.dev/source/nexantic.git/core/internal/consensus/ca"
	"github.com/pkg/errors"
	"go.etcd.io/etcd/clientv3"
	"go.etcd.io/etcd/clientv3/namespace"
	"go.etcd.io/etcd/embed"
	"go.etcd.io/etcd/etcdserver/api/membership"
	"go.etcd.io/etcd/pkg/types"
	"go.etcd.io/etcd/proxy/grpcproxy/adapter"
	"go.uber.org/zap"
	"golang.org/x/sys/unix"
	)

	const (
	DefaultClusterToken = "SIGNOS"
	DefaultLogger = "zap"
	)

	const (
	CAPath = "ca.pem"
	CertPath = "cert.pem"
	KeyPath = "cert-key.pem"
	CRLPath = "ca-crl.der"
	CRLSwapPath = "ca-crl.der.swp"
	)

	const (
	LocalListenerURL = "unix:///consensus/listener.sock:0"
	)

	type (
	Service struct {
	*service.BaseService

	etcd *embed.Etcd
	kv clientv3.KV
	ready bool

	// bootstrapCA and bootstrapCert cache the etcd cluster CA data during bootstrap.
	bootstrapCA *ca.CA
	bootstrapCert []byte

	watchCRLTicker *time.Ticker
	lastCRL []byte

	config *Config
	}

	Config struct {
	Name string
	DataDir string
	InitialCluster string
	NewCluster bool
	ExternalHost string
	ListenHost string
	}

	Member struct {
	ID uint64
	Name string
	Address string
	Synced bool
	}
	)

	func NewConsensusService(config Config, logger zap.Logger) (Service, error) {
	consensusServer := &Service{
	config: &config,
	}
	consensusServer.BaseService = service.NewBaseService("consensus", logger, consensusServer)

	return consensusServer, nil
	}

	func (s *Service) OnStart() error {
	// See: https://godoc.org/github.com/coreos/etcd/embed#Config

	if s.config == nil {
	return errors.New("config for consensus is nil")
	}

	cfg := embed.NewConfig()

	cfg.PeerTLSInfo.CertFile = filepath.Join(s.config.DataDir, CertPath)
	cfg.PeerTLSInfo.KeyFile = filepath.Join(s.config.DataDir, KeyPath)
	cfg.PeerTLSInfo.TrustedCAFile = filepath.Join(s.config.DataDir, CAPath)
	cfg.PeerTLSInfo.ClientCertAuth = true
	cfg.PeerTLSInfo.CRLFile = filepath.Join(s.config.DataDir, CRLPath)

	lastCRL, err := ioutil.ReadFile(cfg.PeerTLSInfo.CRLFile)
	if err != nil {
	return fmt.Errorf("failed to read etcd CRL: %w", err)
	}
	s.lastCRL = lastCRL

	// Expose etcd to local processes
	if err := os.MkdirAll("/consensus", 0700); err != nil {
	return fmt.Errorf("Failed to create consensus runtime state directory: %w", err)
	}
	listenerURL, err := url.Parse(LocalListenerURL)
	if err != nil {
	panic(err)
	}
	cfg.LCUrls = []url.URL{*listenerURL}

	// Advertise Peer URLs
	apURL, err := url.Parse(fmt.Sprintf("https://%s:%d", s.config.ExternalHost, common.ConsensusPort))
	if err != nil {
	return fmt.Errorf("invalid external_host or listen_port: %w", err)
	}

	// Listen Peer URLs
	lpURL, err := url.Parse(fmt.Sprintf("https://%s:%d", s.config.ListenHost, common.ConsensusPort))
	if err != nil {
	return fmt.Errorf("invalid listen_host or listen_port: %w", err)
	}
	cfg.APUrls = []url.URL{*apURL}
	cfg.LPUrls = []url.URL{*lpURL}
	cfg.ACUrls = []url.URL{}

	cfg.Dir = s.config.DataDir
	cfg.InitialClusterToken = DefaultClusterToken
	cfg.Name = s.config.Name

	// Only relevant if creating or joining a cluster; otherwise settings will be ignored
	if s.config.NewCluster {
	cfg.ClusterState = "new"
	cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
	} else if s.config.InitialCluster != "" {
	cfg.ClusterState = "existing"
	cfg.InitialCluster = s.config.InitialCluster
	}

	cfg.Logger = DefaultLogger

	server, err := embed.StartEtcd(cfg)
	if err != nil {
	return err
	}
	s.etcd = server

	// Override the logger
	//server.GetLogger() = s.Logger.With(zap.String("component", "etcd"))
	// TODO(leo): can we uncomment this?

	go func() {
	s.Logger.Info("waiting for etcd to become ready")
	<-s.etcd.Server.ReadyNotify()
	s.Logger.Info("etcd is now ready")
	}()

	// Inject kv client
	s.kv = clientv3.NewKVFromKVClient(adapter.KvServerToKvClient(s.etcd.Server), nil)

	// Start CRL watcher
	go s.watchCRL()

	return nil
	}

	// WriteCertificateFiles writes the given node certificate data to local storage
	// such that it can be used by the embedded etcd server.
	// Unfortunately, we cannot pass the certificates directly to etcd.
	func (s Service) WriteCertificateFiles(certs api.ConsensusCertificates) error {
	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CRLPath), certs.Crl, 0600); err != nil {
	return err
	}
	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CertPath),
	pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certs.Cert}), 0600); err != nil {
	return err
	}
	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, KeyPath),
	pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: certs.Key}), 0600); err != nil {
	return err
	}
	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CAPath),
	pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certs.Ca}), 0600); err != nil {
	return err
	}
	return nil
	}

	// PrecreateCA generates the etcd cluster certificate authority and writes it to local storage.
	func (s *Service) PrecreateCA() error {
	// Provision an etcd CA
	etcdRootCA, err := ca.New("Smalltown etcd Root CA")
	if err != nil {
	return err
	}
	cert, privkey, err := etcdRootCA.IssueCertificate(s.config.ExternalHost)
	if err != nil {
	return fmt.Errorf("failed to self-issue a certificate: %w", err)
	}
	if err := os.MkdirAll(s.config.DataDir, 0700); err != nil {
	return fmt.Errorf("failed to create consensus data dir: %w", err)
	}
	// Preserve certificate for later injection
	s.bootstrapCert = cert
	if err := s.WriteCertificateFiles(&api.ConsensusCertificates{
	Ca: etcdRootCA.CACertRaw,
	Crl: etcdRootCA.CRLRaw,
	Cert: cert,
	Key: privkey,
	}); err != nil {
	return fmt.Errorf("failed to setup certificates: %w", err)
	}
	s.bootstrapCA = etcdRootCA
	return nil
	}

	const (
	caPathEtcd = "/etcd-ca/ca.der"
	caKeyPathEtcd = "/etcd-ca/ca-key.der"
	crlPathEtcd = "/etcd-ca/crl.der"

	// This prefix stores the individual certs the etcd CA has issued.
	certPrefixEtcd = "/etcd-ca/certs"
	)

	// InjectCA copies the CA from data cached during PrecreateCA to etcd.
	// Requires a previous call to PrecreateCA.
	func (s *Service) InjectCA() error {
	if s.bootstrapCA == nil \|\| s.bootstrapCert == nil {
	panic("bootstrapCA or bootstrapCert are nil - missing PrecreateCA call?")
	}
	if _, err := s.kv.Put(context.Background(), caPathEtcd, string(s.bootstrapCA.CACertRaw)); err != nil {
	return err
	}
	// TODO(lorenz): Should be wrapped by the master key
	if _, err := s.kv.Put(context.Background(), caKeyPathEtcd, string([]byte(*s.bootstrapCA.PrivateKey))); err != nil {
	return err
	}
	if _, err := s.kv.Put(context.Background(), crlPathEtcd, string(s.bootstrapCA.CRLRaw)); err != nil {
	return err
	}
	certVal, err := x509.ParseCertificate(s.bootstrapCert)
	if err != nil {
	return err
	}
	serial := hex.EncodeToString(certVal.SerialNumber.Bytes())
	if _, err := s.kv.Put(context.Background(), path.Join(certPrefixEtcd, serial), string(s.bootstrapCert)); err != nil {
	return fmt.Errorf("failed to persist certificate: %w", err)
	}
	// Clear out bootstrap CA after injecting
	s.bootstrapCA = nil
	s.bootstrapCert = []byte{}
	return nil
	}

	func (s *Service) etcdGetSingle(path string) ([]byte, int64, error) {
	res, err := s.kv.Get(context.Background(), path)
	if err != nil {
	return nil, -1, fmt.Errorf("failed to get key from etcd: %w", err)
	}
	if len(res.Kvs) != 1 {
	return nil, -1, errors.New("key not available or multiple keys returned")
	}
	return res.Kvs[0].Value, res.Kvs[0].ModRevision, nil
	}

	func (s Service) getCAFromEtcd() (ca.CA, int64, error) {
	// TODO: Technically this could be done in a single request, but it's more logic
	caCert, _, err := s.etcdGetSingle(caPathEtcd)
	if err != nil {
	return nil, -1, fmt.Errorf("failed to get CA certificate from etcd: %w", err)
	}
	caKey, _, err := s.etcdGetSingle(caKeyPathEtcd)
	if err != nil {
	return nil, -1, fmt.Errorf("failed to get CA key from etcd: %w", err)
	}
	// TODO: Unwrap CA key once wrapping is implemented
	crl, crlRevision, err := s.etcdGetSingle(crlPathEtcd)
	if err != nil {
	return nil, -1, fmt.Errorf("failed to get CRL from etcd: %w", err)
	}
	idCA, err := ca.FromCertificates(caCert, caKey, crl)
	if err != nil {
	return nil, -1, fmt.Errorf("failed to take CA online: %w", err)
	}
	return idCA, crlRevision, nil
	}

	func (s Service) IssueCertificate(hostname string) (api.ConsensusCertificates, error) {
	idCA, _, err := s.getCAFromEtcd()
	if err != nil {
	return nil, err
	}
	cert, key, err := idCA.IssueCertificate(hostname)
	if err != nil {
	return nil, fmt.Errorf("failed to issue certificate: %w", err)
	}
	certVal, err := x509.ParseCertificate(cert)
	if err != nil {
	return nil, err
	}
	serial := hex.EncodeToString(certVal.SerialNumber.Bytes())
	if _, err := s.kv.Put(context.Background(), path.Join(certPrefixEtcd, serial), string(cert)); err != nil {
	// We issued a certificate, but failed to persist it. Return an error and forget it ever happened.
	return nil, fmt.Errorf("failed to persist certificate: %w", err)
	}
	return &api.ConsensusCertificates{
	Ca: idCA.CACertRaw,
	Cert: cert,
	Crl: idCA.CRLRaw,
	Key: key,
	}, nil
	}

	func (s *Service) RevokeCertificate(hostname string) error {
	rand.Seed(time.Now().UnixNano())
	for {
	idCA, crlRevision, err := s.getCAFromEtcd()
	if err != nil {
	return err
	}
	allIssuedCerts, err := s.kv.Get(context.Background(), certPrefixEtcd, clientv3.WithPrefix())
	for _, cert := range allIssuedCerts.Kvs {
	certVal, err := x509.ParseCertificate(cert.Value)
	if err != nil {
	s.Logger.Error("Failed to parse previously issued certificate, this is a security risk", zap.Error(err))
	continue
	}
	for _, dnsName := range certVal.DNSNames {
	if dnsName == hostname {
	// Revoke this
	if err := idCA.Revoke(certVal.SerialNumber); err != nil {
	// We need to fail if any single revocation fails otherwise outer applications
	// have no chance of calling this safely
	return err
	}
	}
	}
	}
	// TODO(leo): this needs a test
	cmp := clientv3.Compare(clientv3.ModRevision(crlPathEtcd), "=", crlRevision)
	op := clientv3.OpPut(crlPathEtcd, string(idCA.CRLRaw))
	res, err := s.kv.Txn(context.Background()).If(cmp).Then(op).Commit()
	if err != nil {
	return fmt.Errorf("failed to persist new CRL in etcd: %w", err)
	}
	if res.Succeeded { // Transaction has succeeded
	break
	}
	// Sleep a random duration between 0 and 300ms to reduce serialization failures
	time.Sleep(time.Duration(rand.Intn(300)) * time.Millisecond)
	}
	return nil
	}

	func (s *Service) watchCRL() {
	// TODO(lorenz): Change etcd client to WatchableKV and make this an actual watch
	// This needs changes in more places, so leaving it now
	s.watchCRLTicker = time.NewTicker(30 * time.Second)
	for range s.watchCRLTicker.C {
	crl, _, err := s.etcdGetSingle(crlPathEtcd)
	if err != nil {
	s.Logger.Warn("Failed to check for new CRL", zap.Error(err))
	continue
	}
	// This is cryptographic material but not secret, so no constant time compare necessary here
	if !bytes.Equal(crl, s.lastCRL) {
	if err := ioutil.WriteFile(filepath.Join(s.config.DataDir, CRLSwapPath), crl, 0600); err != nil {
	s.Logger.Warn("Failed to write updated CRL", zap.Error(err))
	}
	// This uses unix.Rename to guarantee a particular atomic update behavior
	if err := unix.Rename(filepath.Join(s.config.DataDir, CRLSwapPath), filepath.Join(s.config.DataDir, CRLPath)); err != nil {
	s.Logger.Warn("Failed to atomically swap updated CRL", zap.Error(err))
	}
	}
	}
	}

	func (s *Service) OnStop() error {
	s.watchCRLTicker.Stop()
	s.etcd.Close()

	return nil
	}

	// IsProvisioned returns whether the node has been setup before and etcd has a data directory
	func (s *Service) IsProvisioned() bool {
	_, err := os.Stat(s.config.DataDir)

	return !os.IsNotExist(err)
	}

	// IsReady returns whether etcd is ready and synced
	func (s *Service) IsReady() bool {
	return s.ready
	}

	// AddMember adds a new etcd member to the cluster
	func (s *Service) AddMember(ctx context.Context, name string, url string) (uint64, error) {
	urls, err := types.NewURLs([]string{url})
	if err != nil {
	return 0, err
	}

	member := membership.NewMember(name, urls, DefaultClusterToken, nil)

	_, err = s.etcd.Server.AddMember(ctx, *member)
	if err != nil {
	return 0, err
	}

	return uint64(member.ID), nil
	}

	// RemoveMember removes a member from the etcd cluster
	func (s *Service) RemoveMember(ctx context.Context, id uint64) error {
	_, err := s.etcd.Server.RemoveMember(ctx, id)
	return err
	}

	// Health returns the current cluster health
	func (s *Service) Health() {
	}

	// GetConfig returns the current consensus config
	func (s *Service) GetConfig() Config {
	return *s.config
	}

	// SetConfig sets the consensus config. Changes are only applied when the service is restarted.
	func (s *Service) SetConfig(config Config) {
	s.config = &config
	}

	// GetInitialClusterString returns the InitialCluster string that can be used to bootstrap a consensus node
	func (s *Service) GetInitialClusterString() string {
	members := s.etcd.Server.Cluster().Members()
	clusterString := strings.Builder{}

	for i, m := range members {
	if i != 0 {
	clusterString.WriteString(",")
	}
	clusterString.WriteString(m.Name)
	clusterString.WriteString("=")
	clusterString.WriteString(m.PickPeerURL())
	}

	return clusterString.String()
	}

	// GetNodes returns a list of consensus nodes
	func (s *Service) GetNodes() []Member {
	members := s.etcd.Server.Cluster().Members()
	cMembers := make([]Member, len(members))
	for i, m := range members {
	cMembers[i] = Member{
	ID: uint64(m.ID),
	Name: m.Name,
	Address: m.PickPeerURL(),
	Synced: !m.IsLearner,
	}
	}

	return cMembers
	}

	func (s *Service) GetStore(module, space string) clientv3.KV {
	return namespace.NewKV(s.kv, fmt.Sprintf("%s:%s", module, space))
	}