FEAT: Added Redis Caching

discovery/go.mod

@@ -3,8 +3,11 @@ module thamanyah/discovery
 go 1.25.12
 
 require (
+	github.com/aws/aws-sdk-go-v2/config v1.33.1
+	github.com/aws/aws-sdk-go-v2/service/sqs v1.48.1
 	github.com/golang-migrate/migrate/v4 v4.19.1
 	github.com/lib/pq v1.12.3
+	github.com/redis/go-redis/v9 v9.22.0
 	github.com/swaggo/http-swagger/v2 v2.0.2
 	github.com/swaggo/swag v1.16.6
 )
@@ -12,7 +15,6 @@ require (
 require (
 	github.com/KyleBanks/depth v1.2.1 // indirect
 	github.com/aws/aws-sdk-go-v2 v1.45.1 // indirect
-	github.com/aws/aws-sdk-go-v2/config v1.33.1 // indirect
 	github.com/aws/aws-sdk-go-v2/credentials v1.20.1 // indirect
 	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.19.1 // indirect
 	github.com/aws/aws-sdk-go-v2/internal/configsources v1.5.1 // indirect
@@ -21,11 +23,11 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.19 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.14.1 // indirect
 	github.com/aws/aws-sdk-go-v2/service/signin v1.7.1 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sqs v1.48.1 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sso v1.35.1 // indirect
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.40.1 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.47.1 // indirect
 	github.com/aws/smithy-go v1.28.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/go-openapi/jsonpointer v0.19.5 // indirect
 	github.com/go-openapi/jsonreference v0.20.0 // indirect
 	github.com/go-openapi/spec v0.20.6 // indirect
@@ -33,8 +35,10 @@ require (
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/mailru/easyjson v0.7.6 // indirect
 	github.com/swaggo/files/v2 v2.0.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
 	golang.org/x/mod v0.29.0 // indirect
 	golang.org/x/sync v0.18.0 // indirect
+	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/tools v0.38.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )

discovery/go.sum

@@ -34,6 +34,12 @@ github.com/aws/aws-sdk-go-v2/service/sts v1.47.1 h1:Sv2xPnRHlThSUtVujYuUBPI/Il8s
 github.com/aws/aws-sdk-go-v2/service/sts v1.47.1/go.mod h1:mKo/CzaCz8qytGW70NG4vIIGAx1HXTlb5lHNkC5k3lk=
 github.com/aws/smithy-go v1.28.1 h1:R/nXH00c8qcfCzQVELtRw+eLQWtzv+VAIEFJ1/xxXlQ=
 github.com/aws/smithy-go v1.28.1/go.mod h1:YE2RhdIuDbA5E5bTdciG9KrW3+TiEONeUWCqxX9i1Fc=
+github.com/bsm/ginkgo/v2 v2.12.0 h1:Ny8MWAHyOepLGlLKYmXG4IEkioBysk6GpaRTLC8zwWs=
+github.com/bsm/ginkgo/v2 v2.12.0/go.mod h1:SwYbGRRDovPVboqFv0tPTcG1sN61LM1Z4ARdbAV9g4c=
+github.com/bsm/gomega v1.27.10 h1:yeMWxP2pV2fG3FgAODIY8EiRE3dy0aeFYt4l7wh6yKA=
+github.com/bsm/gomega v1.27.10/go.mod h1:JyEr/xRbxbtgWNi8tIEVPUYZ5Dzef52k01W3YH0H+O0=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/containerd/errdefs v1.0.0 h1:tg5yIfIlQIrxYtu9ajqY42W3lpS19XqdxRQeEwYG8PI=
 github.com/containerd/errdefs v1.0.0/go.mod h1:+YBYIdtsnF4Iw6nWZhJcqGSg/dwvV7tyJ/kCkyJ2k+M=
 github.com/containerd/errdefs/pkg v0.3.0 h1:9IKJ06FvyNlexW690DXuQNx2KA2cUJXx151Xdx3ZPPE=
@@ -77,6 +83,8 @@ github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/josharian/intern v1.0.0 h1:vlS4z54oSdjm0bgjRigI+G1HpF+tI+9rE5LLzOg8HmY=
 github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
+github.com/klauspost/cpuid/v2 v2.2.10 h1:tBs3QSyvjDyFTq3uoc/9xFpCuOsJQFNPiAhYdw2skhE=
+github.com/klauspost/cpuid/v2 v2.2.10/go.mod h1:hqwkgyIinND0mEev00jJYCxPNVRVXFQeu1XKlok6oO0=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
@@ -105,6 +113,8 @@ github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/redis/go-redis/v9 v9.22.0 h1:laDvpYXTJtZLloinw1fA5Kqd6HAEH2XKxOkG/PDq2F0=
+github.com/redis/go-redis/v9 v9.22.0/go.mod h1:y2g0Wj8rQvuK0ELM+oxSudcLtC09JScs98I/X9gRWY4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
@@ -116,6 +126,8 @@ github.com/swaggo/http-swagger/v2 v2.0.2 h1:FKCdLsl+sFCx60KFsyM0rDarwiUSZ8DqbfSy
 github.com/swaggo/http-swagger/v2 v2.0.2/go.mod h1:r7/GBkAWIfK6E/OLnE8fXnviHiDeAHmgIyooa4xm3AQ=
 github.com/swaggo/swag v1.16.6 h1:qBNcx53ZaX+M5dxVyTrgQ0PJ/ACK+NzhwcbieTt+9yI=
 github.com/swaggo/swag v1.16.6/go.mod h1:ngP2etMK5a0P3QBizic5MEwpRmluJZPHjXcMoj4Xesg=
+github.com/zeebo/xxh3 v1.1.0 h1:s7DLGDK45Dyfg7++yxI0khrfwq9661w9EN78eP/UZVs=
+github.com/zeebo/xxh3 v1.1.0/go.mod h1:IisAie1LELR4xhVinxWS5+zf1lA4p0MW4T+w+W07F5s=
 go.opentelemetry.io/auto/sdk v1.1.0 h1:cH53jehLUN6UFLY71z+NDOiNJqDdPRaXzTel0sJySYA=
 go.opentelemetry.io/auto/sdk v1.1.0/go.mod h1:3wSPjt5PWp2RhlCcmmOial7AvC4DQqZb7a7wCow3W8A=
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.61.0 h1:F7Jx+6hwnZ41NSFTO5q4LYDtJRXBf2PD0rNBkeB/lus=
@@ -126,6 +138,8 @@ go.opentelemetry.io/otel/metric v1.37.0 h1:mvwbQS5m0tbmqML4NqK+e3aDiO02vsf/Wgbsd
 go.opentelemetry.io/otel/metric v1.37.0/go.mod h1:04wGrZurHYKOc+RKeye86GwKiTb9FKm1WHtO+4EVr2E=
 go.opentelemetry.io/otel/trace v1.37.0 h1:HLdcFNbRQBE2imdSEgm/kwqmQj1Or1l/7bW6mxVK7z4=
 go.opentelemetry.io/otel/trace v1.37.0/go.mod h1:TlgrlQ+PtQO5XFerSPUYG0JSgGyryXewPGyayAWSBS0=
+go.uber.org/atomic v1.11.0 h1:ZvwS0R+56ePWxUNi+Atn9dWONBPp/AUETXlHW0DxSjE=
+go.uber.org/atomic v1.11.0/go.mod h1:LUxbIzbOniOlMKjJjyPfpl4v+PKK2cNJn91OQbhoJI0=
 golang.org/x/mod v0.29.0 h1:HV8lRxZC4l2cr3Zq1LvtOsi/ThTgWnUk/y64QSs8GwA=
 golang.org/x/mod v0.29.0/go.mod h1:NyhrlYXJ2H4eJiRy/WDBO6HMqZQ6q9nk4JzS3NuCK+w=
 golang.org/x/sync v0.18.0 h1:kr88TuHDroi+UVf+0hZnirlk8o8T+4MrK6mr60WkH/I=

discovery/internal/handlers/videos.go

@@ -1,12 +1,17 @@
 package handlers
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"log"
 	"net/http"
+	"slices"
+	"strings"
 	"thamanyah/discovery/internal/api"
 	"thamanyah/discovery/internal/db/repositories"
+	"thamanyah/discovery/internal/services"
+	"time"
 )
 
 // GetVideo serves the catalogue's copy of one video.
@@ -64,8 +69,112 @@ const (
 	// cursor still reaches the rest — because a client that wants everything
 	// is doing something legitimate, just not in one request.
 	maxSearchPageSize = 100
+
+	// searchCacheTTL is how long a page of results stays servable from the
+	// cache before it has to be built again.
+	//
+	// Nothing invalidates an entry when a video is announced: the consumer
+	// writes rows continuously and would have to know which of the cached
+	// pages a new title belongs on, which for a ranked search is every page it
+	// outranks. Expiry is the cheaper answer, and it bounds the staleness — a
+	// video is findable within a minute of being catalogued, which is the same
+	// order as the announcement's own delivery lag.
+	searchCacheTTL = time.Minute
 )
 
+// searchCacheKey is what one page of search results is stored under: the title
+// searched for, the categories it was narrowed to, and the page within that
+// result set.
+//
+// The page is named by the cursor, because with keyset paging that is what a
+// page *is* — there is no page number to key on, and the cursor identifies the
+// same rows whenever it is presented. The empty cursor is the first page.
+//
+// The limit is in the key too, even though a reader would not call it part of
+// "which page". It has to be: the same title, categories and cursor with a
+// different limit is a different set of rows, and sharing an entry between
+// them would hand a client asking for 50 a page of 20.
+//
+// The parts are JSON-encoded rather than pasted together with separators so
+// that no category name can be mistaken for the boundary between two of them —
+// {"c":["a,b"]} and {"c":["a","b"]} stay distinguishable, which "a,b" and
+// "a,b" would not. The key stays readable in redis-cli either way.
+func searchCacheKey(title string, categories []string, limit int, cursor string) string {
+	// The title is lowercased because the search itself is: tsQueryFor folds
+	// case before it builds the tsquery, so two spellings that differ only in
+	// case are the same search and should be the same entry. The categories
+	// are not — they are compared to the stored array verbatim, so "News" and
+	// "news" really do ask different questions.
+	//
+	// Sorting the categories is safe for the same reason the SQL uses &&:
+	// they mean "any of these", so their order never changed the answer. Two
+	// readers naming the same categories in a different order now share one
+	// entry instead of building the same page twice.
+	//
+	// Never nil, so that a client sending "categories": [] and one omitting
+	// the member entirely — the same search, since both mean "every category"
+	// — land on one entry rather than on `null` and `[]`.
+	sorted := append([]string{}, categories...)
+	slices.Sort(sorted)
+	sorted = slices.Compact(sorted)
+
+	parts := struct {
+		Title      string   `json:"t"`
+		Categories []string `json:"c"`
+		Limit      int      `json:"l"`
+		Cursor     string   `json:"p"`
+	}{
+		Title:      strings.ToLower(strings.TrimSpace(title)),
+		Categories: sorted,
+		Limit:      limit,
+		Cursor:     cursor,
+	}
+
+	// Cannot fail: every field is a string, a string slice or an int.
+	encoded, _ := json.Marshal(parts)
+	return "discovery:search:v1:" + string(encoded)
+}
+
+// cachedSearch returns the page held under key, or false when there is none to
+// serve.
+//
+// Every failure reads as "no cached page": a cache that is unreachable, slow
+// or holding something unreadable must cost a reader nothing more than the
+// database query they would have paid for anyway. Only faults worth acting on
+// are logged — a miss is not one.
+func cachedSearch(ctx context.Context, key string) (api.SearchResults, bool) {
+	encoded, err := services.CacheClient.Get(ctx, key)
+	if errors.Is(err, services.ErrCacheMiss) {
+		return api.SearchResults{}, false
+	}
+	if err != nil {
+		log.Printf("Could Not Read The Search Cache, Falling Back To The Database: key=%q: %s", key, err)
+		return api.SearchResults{}, false
+	}
+
+	var results api.SearchResults
+	if err := json.Unmarshal(encoded, &results); err != nil {
+		// Only reachable if something else wrote this key, or the shape
+		// changed without the v1 in the prefix changing with it.
+		log.Printf("Could Not Read A Cached Search Page, Falling Back To The Database: key=%q: %s", key, err)
+		return api.SearchResults{}, false
+	}
+
+	return results, true
+}
+
+func cacheSearch(ctx context.Context, key string, results api.SearchResults) {
+	encoded, err := json.Marshal(results)
+	if err != nil {
+		log.Printf("Could Not Encode A Search Page For The Cache: key=%q: %s", key, err)
+		return
+	}
+
+	if err := services.CacheClient.Set(ctx, key, encoded, searchCacheTTL); err != nil {
+		log.Printf("Could Not Write The Search Cache: key=%q: %s", key, err)
+	}
+}
+
 // SearchVideos serves the catalogue's lexical search.
 //
 // It is served on QUERY rather than GET or POST: a search is safe and
@@ -94,6 +203,19 @@ func SearchVideos(w http.ResponseWriter, r *http.Request) {
 		limit = maxSearchPageSize
 	}
 
+	// Read through the cache before touching Postgres. A ranked search is the
+	// expensive request this service serves — ts_rank is computed per matching
+	// row, so deep pages scan rather than seek — and readers ask for the same
+	// few things over and over, which is exactly the shape a cache pays for.
+	//
+	// Only successful pages are ever stored, so a malformed cursor still
+	// reaches the repository and is still rejected below.
+	cacheKey := searchCacheKey(request.Title, request.Categories, limit, request.Cursor)
+	if cached, hit := cachedSearch(r.Context(), cacheKey); hit {
+		writeJSON(w, http.StatusOK, cached)
+		return
+	}
+
 	found, next, err := repositories.VideoRepo.SearchVideos(r.Context(), request.Title, request.Categories, limit, request.Cursor)
 	if errors.Is(err, repositories.ErrInvalidCursor) {
 		writeProblem(w, http.StatusBadRequest, "Malformed Search Cursor",
@@ -119,5 +241,8 @@ func SearchVideos(w http.ResponseWriter, r *http.Request) {
 		})
 	}
 
-	writeJSON(w, http.StatusOK, api.SearchResults{Videos: videos, NextCursor: next})
+	results := api.SearchResults{Videos: videos, NextCursor: next}
+	cacheSearch(r.Context(), cacheKey, results)
+
+	writeJSON(w, http.StatusOK, results)
 }

discovery/internal/services/cache.go

@@ -0,0 +1,58 @@
+package services
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/redis/go-redis/v9"
+)
+
+var CacheClient Cache
+
+var ErrCacheMiss = errors.New("cache: miss")
+
+type Cache interface {
+	Get(ctx context.Context, key string) ([]byte, error)
+	Set(ctx context.Context, key string, value []byte, ttl time.Duration) error
+}
+
+type RedisConcrete struct {
+	Redis *redis.Client
+}
+
+const cacheOperationTimeout = 100 * time.Millisecond
+
+func (svc RedisConcrete) Get(ctx context.Context, key string) ([]byte, error) {
+	ctx, cancel := context.WithTimeout(ctx, cacheOperationTimeout)
+	defer cancel()
+
+	value, err := svc.Redis.Get(ctx, key).Bytes()
+	if errors.Is(err, redis.Nil) {
+		return nil, ErrCacheMiss
+	}
+	if err != nil {
+		return nil, err
+	}
+	return value, nil
+}
+
+func (svc RedisConcrete) Set(ctx context.Context, key string, value []byte, ttl time.Duration) error {
+	ctx, cancel := context.WithTimeout(ctx, cacheOperationTimeout)
+	defer cancel()
+
+	return svc.Redis.Set(ctx, key, value, ttl).Err()
+}
+
+func (svc RedisConcrete) Close() error {
+	return svc.Redis.Close()
+}
+
+func (svc RedisConcrete) AssertSuccessfulConnection(ctx context.Context) {
+	if err := svc.Redis.Ping(ctx).Err(); err != nil {
+		log.Printf("WARNING: %s", fmt.Errorf("redis: cannot reach cache at %q, searches will be served from the database: %w",
+			svc.Redis.Options().Addr, err))
+	}
+}

discovery/main.go

@@ -11,10 +11,12 @@ import (
 	"thamanyah/discovery/internal/db/repositories"
 	"thamanyah/discovery/internal/handlers"
 	"thamanyah/discovery/internal/services"
+	"time"
 
 	awsconfig "github.com/aws/aws-sdk-go-v2/config"
 	"github.com/aws/aws-sdk-go-v2/service/sqs"
 	_ "github.com/lib/pq"
+	"github.com/redis/go-redis/v9"
 	httpSwagger "github.com/swaggo/http-swagger/v2"
 
 	_ "thamanyah/discovery/docs"
@@ -65,6 +67,38 @@ func runServer() {
 
 	services.SQSClient = concreteSQSClient
 
+	// The ElastiCache Redis node the catalogue search is answered from. Not an
+	// AWS API call — the address resolves inside the VPC and the security
+	// group is what grants access — so it needs nothing from the task role and
+	// nothing from awsConfig.
+	//
+	// The address is required because a missing one is a deployment mistake,
+	// not a choice; whether the node actually answers is a different question,
+	// and one the service deliberately survives getting "no" to.
+	redisAddress := os.Getenv("REDIS_ADDR")
+	if redisAddress == "" {
+		panic(fmt.Errorf("missing required env var: REDIS_ADDR"))
+	}
+
+	concreteCacheClient := &services.RedisConcrete{
+		Redis: redis.NewClient(&redis.Options{
+			Addr: redisAddress,
+			// Per-call deadlines on top of the budget RedisConcrete already
+			// applies, so a connection that hangs rather than refusing cannot
+			// tie up a goroutine past the request that opened it. Retries are
+			// off for the same reason the budget is small: a second attempt at
+			// a cache costs more than the query it is saving.
+			DialTimeout:  100 * time.Millisecond,
+			ReadTimeout:  100 * time.Millisecond,
+			WriteTimeout: 100 * time.Millisecond,
+			MaxRetries:   -1,
+		}),
+	}
+	defer func() { _ = concreteCacheClient.Close() }()
+	concreteCacheClient.AssertSuccessfulConnection(context.Background())
+
+	services.CacheClient = concreteCacheClient
+
 	concreteDBClient := db.CreateDBConnection(requireDBConnectionString())
 	defer db.CloseConnection(concreteDBClient)
 	db.AssertSuccessfulConnection(context.Background(), concreteDBClient)