First draft of discovery

go/cmd/vtgateproxy/vtgateproxy.go

@@ -38,11 +38,12 @@ func main() {
 	servenv.ParseFlags("vtgateproxy")
 	servenv.Init()
 
-	vtgateproxy.Init()
-
 	servenv.OnRun(func() {
 		// Flags are parsed now. Parse the template using the actual flag value and overwrite the current template.
+		vtgateproxy.RegisterJsonDiscovery()
+		vtgateproxy.Init()
 	})
+
 	servenv.OnClose(func() {
 	})
 	servenv.RunDefault()

go/vt/vtgateproxy/discovery.go

@@ -0,0 +1,212 @@
+package vtgateproxy
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"math/rand"
+	"os"
+	"strconv"
+	"time"
+
+	"google.golang.org/grpc/resolver"
+)
+
+var (
+	jsonDiscoveryConfig = flag.String("json_config", "", "json file describing the host list to use fot vitess://vtgate resolution")
+)
+
+// File based discovery for vtgate grpc endpoints
+// This loads the list of hosts from json and watches for changes to the list of hosts. It will select N connection to maintain to backend vtgates.
+// Connections will rebalance every 5 minutes
+//
+// Example json config - based on the slack hosts format
+//
+// [
+//     {
+//         "address": "10.4.56.194",
+//         "az_id": "use1-az1",
+//         "grpc": "15999",
+//         "type": "aux"
+//     },
+//
+// Naming scheme:
+// vtgate://<type>?num_connections=<int>&az_id=<string>
+//
+// num_connections: Option number of hosts to open connections to for round-robin selection
+// az_id: Filter to just hosts in this az (optional)
+// type: Only select from hosts of this type (required)
+//
+
+type DiscoveryHost struct {
+	Address string
+	Grpc    string
+	AZ_Id   string `json:az_id`
+	Type    string
+}
+
+type JSONGateConfigDiscovery struct {
+	JsonPath string
+}
+
+func (b *JSONGateConfigDiscovery) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
+	queryOpts := target.URL.Query()
+	queryParamCount := queryOpts.Get("num_connections")
+	queryAZID := queryOpts.Get("az_id")
+	num_connections := 0
+
+	gateType := target.URL.Host
+
+	if queryParamCount != "" {
+		num_connections, _ = strconv.Atoi(queryParamCount)
+	}
+
+	filters := resolveFilters{
+		gate_type: gateType,
+	}
+
+	if queryAZID != "" {
+		filters.az_id = queryAZID
+	}
+
+	r := &resolveJSONGateConfig{
+		target:          target,
+		cc:              cc,
+		jsonPath:        b.JsonPath,
+		num_connections: num_connections,
+		filters:         filters,
+	}
+	r.start()
+	return r, nil
+}
+func (*JSONGateConfigDiscovery) Scheme() string { return "vtgate" }
+
+func RegisterJsonDiscovery() {
+	fmt.Printf("Registering: %v\n", *jsonDiscoveryConfig)
+	resolver.Register(&JSONGateConfigDiscovery{
+		JsonPath: *jsonDiscoveryConfig,
+	})
+}
+
+type resolveFilters struct {
+	gate_type string
+	az_id     string
+}
+
+// exampleResolver is a
+// Resolver(https://godoc.org/google.golang.org/grpc/resolver#Resolver).
+type resolveJSONGateConfig struct {
+	target          resolver.Target
+	cc              resolver.ClientConn
+	jsonPath        string
+	ticker          *time.Ticker
+	rand            *rand.Rand // safe for concurrent use.
+	num_connections int
+	filters         resolveFilters
+}
+
+func (r *resolveJSONGateConfig) loadConfig() (*[]resolver.Address, error) {
+	config := []DiscoveryHost{}
+
+	data, err := os.ReadFile(r.jsonPath)
+	if err != nil {
+		return nil, err
+	}
+
+	err = json.Unmarshal(data, &config)
+	if err != nil {
+		fmt.Printf("parse err: %v\n", err)
+		return nil, err
+	}
+
+	fmt.Printf("%v\n", config)
+
+	addrs := make([]resolver.Address, len(config))
+	for i, s := range config {
+		// Apply filters
+		if r.filters.gate_type != "" {
+			if r.filters.gate_type != s.Type {
+				fmt.Printf("Dropped non matching type: %v\n", s.Type)
+				continue
+			}
+		}
+
+		if r.filters.az_id != "" {
+			if r.filters.az_id != s.AZ_Id {
+				fmt.Printf("Dropped non matching az: %v\n", s.AZ_Id)
+				continue
+			}
+		}
+		// Add matching hosts to registration list
+		addrs[i] = resolver.Address{Addr: fmt.Sprintf("%s:%s", s.Address, s.Grpc)}
+	}
+
+	// Shuffle to ensure every host has a different order to iterate through
+	r.rand.Shuffle(len(addrs), func(i, j int) {
+		addrs[i], addrs[j] = addrs[j], addrs[i]
+	})
+
+	// Slice off the first N hosts, optionally
+	if r.num_connections > 0 && r.num_connections <= len(addrs) {
+		addrs = addrs[0:r.num_connections]
+	}
+
+	fmt.Printf("Returning discovery: %v\n", addrs)
+
+	return &addrs, nil
+}
+
+func (r *resolveJSONGateConfig) start() {
+	fmt.Print("Starting discovery checker\n")
+	r.rand = rand.New(rand.NewSource(time.Now().UnixNano()))
+
+	// Immediately load the initial config
+	addrs, err := r.loadConfig()
+	if err == nil {
+		// if we parse ok, populate the local address store
+		r.cc.UpdateState(resolver.State{Addresses: *addrs})
+	}
+
+	// Start a config watcher
+	r.ticker = time.NewTicker(100 * time.Millisecond)
+	fileStat, err := os.Stat(r.jsonPath)
+	if err != nil {
+		return
+	}
+	lastLoaded := time.Now()
+
+	go func() {
+		for range r.ticker.C {
+			checkFileStat, err := os.Stat(r.jsonPath)
+			isUnchanged := checkFileStat.Size() == fileStat.Size() || checkFileStat.ModTime() == fileStat.ModTime()
+			isNotExpired := time.Since(lastLoaded) < 1*time.Minute
+			if isUnchanged && isNotExpired {
+				// no change
+				continue
+			}
+			lastLoaded = time.Now()
+
+			fileStat = checkFileStat
+			fmt.Printf("Detected config change\n")
+
+			addrs, err := r.loadConfig()
+			if err != nil {
+				// better luck next loop
+				// TODO: log this
+				fmt.Print("oh no\n")
+				continue
+			}
+
+			r.cc.UpdateState(resolver.State{Addresses: *addrs})
+		}
+	}()
+}
+func (r *resolveJSONGateConfig) ResolveNow(o resolver.ResolveNowOptions) {}
+func (r *resolveJSONGateConfig) Close() {
+	r.ticker.Stop()
+}
+
+func init() {
+	// Register the example ResolverBuilder. This is usually done in a package's
+	// init() function.
+}

go/vt/vtgateproxy/vtgateproxy.go

@@ -54,6 +54,10 @@ func (proxy *VTGateProxy) connect(ctx context.Context) error {
 		return append(opts, grpc.WithBlock()), nil
 	})
 
+	grpcclient.RegisterGRPCDialOptions(func(opts []grpc.DialOption) ([]grpc.DialOption, error) {
+		return append(opts, grpc.WithDefaultServiceConfig(`{"loadBalancingConfig": [{"round_robin":{}}]}`)), nil
+	})
+
 	conn, err := vtgateconn.DialProtocol(ctx, "grpc", *target)
 	if err != nil {
 		return err
@@ -104,8 +108,6 @@ func (proxy *VTGateProxy) StreamExecute(ctx context.Context, session *vtgateconn
 }
 
 func Init() error {
-	vtGateProxy = &VTGateProxy{}
-
 	// XXX maybe add connect timeout?
 	ctx, cancel := context.WithTimeout(context.Background(), *dialTimeout)
 	defer cancel()