Add redis pool to registry webapp

Redis has been integrated with the web application for use with various
services. The configuraiton exposes connection details, timeouts and pool
parameters. Documentation has been updated accordingly.

A few convenience methods have been added to the context package to get loggers
with certain fields, exposing some missing functionality from logrus.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/handlers/app.go

@@ -1,10 +1,12 @@
 package handlers
 
 import (
+	"expvar"
 	"fmt"
 	"net"
 	"net/http"
 	"os"
+	"time"
 
 	"code.google.com/p/go-uuid/uuid"
 	"github.com/docker/distribution"
@@ -19,6 +21,7 @@ import (
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
 	"github.com/docker/distribution/registry/storage/driver/factory"
 	storagemiddleware "github.com/docker/distribution/registry/storage/driver/middleware"
+	"github.com/garyburd/redigo/redis"
 	"github.com/gorilla/mux"
 	"golang.org/x/net/context"
 )
@@ -44,6 +47,8 @@ type App struct {
 		sink   notifications.Sink
 		source notifications.SourceRecord
 	}
+
+	redis *redis.Pool
 }
 
 // Value intercepts calls context.Context.Value, returning the current app id,
@@ -95,6 +100,7 @@ func NewApp(ctx context.Context, configuration configuration.Configuration) *App
 	}
 
 	app.configureEvents(&configuration)
+	app.configureRedis(&configuration)
 
 	app.registry = storage.NewRegistryWithDriver(app.driver)
 	app.registry, err = applyRegistryMiddleware(app.registry, configuration.Middleware["registry"])
@@ -174,6 +180,83 @@ func (app *App) configureEvents(configuration *configuration.Configuration) {
 	}
 }
 
+func (app *App) configureRedis(configuration *configuration.Configuration) {
+	if configuration.Redis.Addr == "" {
+		ctxu.GetLogger(app).Infof("redis not configured")
+		return
+	}
+
+	pool := &redis.Pool{
+		Dial: func() (redis.Conn, error) {
+			// TODO(stevvooe): Yet another use case for contextual timing.
+			ctx := context.WithValue(app, "redis.connect.startedat", time.Now())
+
+			done := func(err error) {
+				logger := ctxu.GetLoggerWithField(ctx, "redis.connect.duration",
+					ctxu.Since(ctx, "redis.connect.startedat"))
+				if err != nil {
+					logger.Errorf("redis: error connecting: %v", err)
+				} else {
+					logger.Infof("redis: connect %v", configuration.Redis.Addr)
+				}
+			}
+
+			conn, err := redis.DialTimeout("tcp",
+				configuration.Redis.Addr,
+				configuration.Redis.DialTimeout,
+				configuration.Redis.ReadTimeout,
+				configuration.Redis.WriteTimeout)
+			if err != nil {
+				ctxu.GetLogger(app).Errorf("error connecting to redis instance %s: %v",
+					configuration.Redis.Addr, err)
+				done(err)
+				return nil, err
+			}
+
+			// authorize the connection
+			if configuration.Redis.Password != "" {
+				if _, err = conn.Do("AUTH", configuration.Redis.Password); err != nil {
+					defer conn.Close()
+					done(err)
+					return nil, err
+				}
+			}
+
+			// select the database to use
+			if configuration.Redis.DB != 0 {
+				if _, err = conn.Do("SELECT", configuration.Redis.DB); err != nil {
+					defer conn.Close()
+					done(err)
+					return nil, err
+				}
+			}
+
+			done(nil)
+			return conn, nil
+		},
+		MaxIdle:     configuration.Redis.Pool.MaxIdle,
+		MaxActive:   configuration.Redis.Pool.MaxActive,
+		IdleTimeout: configuration.Redis.Pool.IdleTimeout,
+		TestOnBorrow: func(c redis.Conn, t time.Time) error {
+			// TODO(stevvooe): We can probably do something more interesting
+			// here with the health package.
+			_, err := c.Do("PING")
+			return err
+		},
+		Wait: false, // if a connection is not avialable, proceed without cache.
+	}
+
+	app.redis = pool
+
+	expvar.Publish("redis", expvar.Func(func() interface{} {
+		return map[string]interface{}{
+			"Config": configuration.Redis,
+			"Active": app.redis.ActiveCount(),
+		}
+	}))
+
+}
+
 func (app *App) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	defer r.Body.Close() // ensure that request body is always closed.