[vtadmin-api] Add static file service discovery implementation

docker/local/run.sh

@@ -1,3 +1,3 @@
 #!/bin/bash
 
-docker run -p 15000:15000 -p 15001:15001 --rm -it vitess/local
+docker run -p 15000:15000 -p 15001:15001 -p 15991:15991 --rm -it vitess/local

go/vt/vtadmin/cluster/discovery/discovery.go

@@ -91,4 +91,5 @@ func New(impl string, cluster *vtadminpb.Cluster, args []string) (Discovery, err
 
 func init() { // nolint:gochecknoinits
 	Register("consul", NewConsul)
+	Register("staticFile", NewStaticFile)
 }

go/vt/vtadmin/cluster/discovery/discovery_static_file.go

@@ -0,0 +1,176 @@
+/*
+Copyright 2020 The Vitess Authors.
+
+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 discovery
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"math/rand"
+
+	"github.com/spf13/pflag"
+	vtadminpb "vitess.io/vitess/go/vt/proto/vtadmin"
+)
+
+// StaticFileDiscovery implements the Discovery interface for "discovering"
+// Vitess components hardcoded in a static JSON file.
+//
+// As an example, here's a minimal JSON file for a single Vitess cluster running locally
+// (such as the one described in https://vitess.io/docs/get-started/local-docker):
+//
+// 		{
+// 			"vtgates": [
+// 				{
+// 					"host": {
+// 						"hostname": "127.0.0.1:15991"
+// 					}
+// 				}
+// 			]
+// 		}
+//
+// For more examples of various static file configurations, see the unit tests.
+type StaticFileDiscovery struct {
+	cluster *vtadminpb.Cluster
+	config  *StaticFileClusterConfig
+	gates   struct {
+		byName map[string]*vtadminpb.VTGate
+		byTag  map[string][]*vtadminpb.VTGate
+	}
+}
+
+// StaticFileClusterConfig configures Vitess components for a single cluster.
+type StaticFileClusterConfig struct {
+	VTGates []*StaticFileVTGateConfig `json:"vtgates,omitempty"`
+}
+
+// StaticFileVTGateConfig contains host and tag information for a single VTGate in a cluster.
+type StaticFileVTGateConfig struct {
+	Host *vtadminpb.VTGate `json:"host"`
+	Tags []string          `json:"tags"`
+}
+
+// NewStaticFile returns a StaticFileDiscovery for the given cluster.
+func NewStaticFile(cluster *vtadminpb.Cluster, flags *pflag.FlagSet, args []string) (Discovery, error) {
+	disco := &StaticFileDiscovery{
+		cluster: cluster,
+	}
+
+	filePath := flags.String("path", "", "path to the service discovery JSON config file")
+	if err := flags.Parse(args); err != nil {
+		return nil, err
+	}
+
+	if filePath == nil || *filePath == "" {
+		return nil, errors.New("must specify path to the service discovery JSON config file")
+	}
+
+	b, err := ioutil.ReadFile(*filePath)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := disco.parseConfig(b); err != nil {
+		return nil, err
+	}
+
+	return disco, nil
+}
+
+func (d *StaticFileDiscovery) parseConfig(bytes []byte) error {
+	if err := json.Unmarshal(bytes, &d.config); err != nil {
+		return err
+	}
+
+	d.gates.byName = make(map[string]*vtadminpb.VTGate, len(d.config.VTGates))
+	d.gates.byTag = make(map[string][]*vtadminpb.VTGate)
+
+	// Index the gates by name and by tag for easier lookups
+	for _, gate := range d.config.VTGates {
+		d.gates.byName[gate.Host.Hostname] = gate.Host
+
+		for _, tag := range gate.Tags {
+			d.gates.byTag[tag] = append(d.gates.byTag[tag], gate.Host)
+		}
+	}
+	return nil
+}
+
+// DiscoverVTGate is part of the Discovery interface.
+func (d *StaticFileDiscovery) DiscoverVTGate(ctx context.Context, tags []string) (*vtadminpb.VTGate, error) {
+	gates, err := d.DiscoverVTGates(ctx, tags)
+	if err != nil {
+		return nil, err
+	}
+
+	count := len(gates)
+	if count == 0 {
+		return nil, ErrNoVTGates
+	}
+
+	gate := gates[rand.Intn(len(gates))]
+	return gate, nil
+}
+
+// DiscoverVTGateAddr is part of the Discovery interface.
+func (d *StaticFileDiscovery) DiscoverVTGateAddr(ctx context.Context, tags []string) (string, error) {
+	gate, err := d.DiscoverVTGate(ctx, tags)
+	if err != nil {
+		return "", err
+	}
+
+	return gate.Hostname, nil
+}
+
+// DiscoverVTGates is part of the Discovery interface.
+func (d *StaticFileDiscovery) DiscoverVTGates(ctx context.Context, tags []string) ([]*vtadminpb.VTGate, error) {
+	if len(tags) == 0 {
+		results := []*vtadminpb.VTGate{}
+		for _, g := range d.gates.byName {
+			results = append(results, g)
+		}
+
+		return results, nil
+	}
+
+	set := d.gates.byName
+
+	for _, tag := range tags {
+		intermediate := map[string]*vtadminpb.VTGate{}
+
+		gates, ok := d.gates.byTag[tag]
+		if !ok {
+			return []*vtadminpb.VTGate{}, nil
+		}
+
+		for _, g := range gates {
+			if _, ok := set[g.Hostname]; ok {
+				intermediate[g.Hostname] = g
+			}
+		}
+
+		set = intermediate
+	}
+
+	results := make([]*vtadminpb.VTGate, 0, len(set))
+
+	for _, gate := range set {
+		results = append(results, gate)
+	}
+
+	return results, nil
+}