frontend: implement cache control (#1974)

* querier: do not cache results if requested

Add an extra `Headers` field to the `PrometheusResponse` message which
contains the headers and their values that came from Prometheus.

Use them in other places to deduce if the response should be cached. If
`Cache-Control` is equal to `no-store` then it is *not* cached.

This will be used by the Thanos project to indicate when a partial
response has been returned. In such cases the result should not be
cached so that invalid data would not be stored there.

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* queryrange: factor out cache checking + add tests

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: gofmt

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: tests: add missing member

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: fix logical mistake

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* queryrange: fix generated code

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: test adjustments

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: test adjustments

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* querier: results_cache: cache by default

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* queryrange: cache: check all header values

`Cache-Control` might contain more than one value so check all of them.

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* Update according to Goutham's comments

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

* CHANGELOG: add full stop, PR's number

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>

CHANGELOG.md

@@ -2,8 +2,8 @@
 
 ## master / unreleased
 
+* [CHANGE] The frontend component now does not cache results if it finds a `Cache-Control` header and if one of its values is `no-store`. #1974
 * [ENHANCEMENT] metric `cortex_ingester_flush_reasons` gets a new `reason` value: `Spread`, when `-ingester.spread-flushes` option is enabled.
-
 * [CHANGE] Flags changed with transition to upstream Prometheus rules manager:
   * `ruler.client-timeout` is now `ruler.configs.client-timeout` in order to match `ruler.configs.url`
   * `ruler.group-timeout`has been removed

pkg/querier/queryrange/query_range.go

@@ -33,6 +33,9 @@ var (
 
 	// PrometheusCodec is a codec to encode and decode Prometheus query range requests and responses.
 	PrometheusCodec Codec = &prometheusCodec{}
+
+	// Name of the cache control header.
+	cachecontrolHeader = "Cache-Control"
 )
 
 // Codec is used to encode/decode query range requests and responses so they can be passed down to middlewares.
@@ -221,6 +224,10 @@ func (prometheusCodec) DecodeResponse(ctx context.Context, r *http.Response, _ R
 	if err := json.Unmarshal(buf, &resp); err != nil {
 		return nil, httpgrpc.Errorf(http.StatusInternalServerError, "error decoding response: %v", err)
 	}
+
+	for h, hv := range r.Header {
+		resp.Headers = append(resp.Headers, &PrometheusResponseHeader{Name: h, Values: hv})
+	}
 	return &resp, nil
 }
 

pkg/querier/queryrange/query_range_test.go

@@ -74,13 +74,15 @@ func TestRequest(t *testing.T) {
 }
 
 func TestResponse(t *testing.T) {
+	r := *parsedResponse
+	r.Headers = respHeaders
 	for i, tc := range []struct {
 		body     string
 		expected *PrometheusResponse
 	}{
 		{
 			body:     responseBody,
-			expected: parsedResponse,
+			expected: &r,
 		},
 	} {
 		t.Run(strconv.Itoa(i), func(t *testing.T) {

pkg/querier/queryrange/queryrange.proto

@@ -21,11 +21,17 @@ message PrometheusRequest {
   string query = 6;
 }
 
+message PrometheusResponseHeader {
+  string Name = 1 [(gogoproto.jsontag) = "-"];
+  repeated string Values = 2 [(gogoproto.jsontag) = "-"];
+}
+
 message PrometheusResponse {
   string Status = 1 [(gogoproto.jsontag) = "status"];
   PrometheusData Data = 2 [(gogoproto.nullable) = false, (gogoproto.jsontag) = "data,omitempty"];
   string ErrorType = 3 [(gogoproto.jsontag) = "errorType,omitempty"];
   string Error = 4 [(gogoproto.jsontag) = "error,omitempty"];
+  repeated PrometheusResponseHeader Headers = 5 [(gogoproto.jsontag) = "-"];
 }
 
 message PrometheusData {

pkg/querier/queryrange/results_cache.go

@@ -22,6 +22,11 @@ import (
 	"github.com/cortexproject/cortex/pkg/util/spanlogger"
 )
 
+var (
+	// Value that cachecontrolHeader has if the response indicates that the results should not be cached.
+	noCacheValue = "no-store"
+)
+
 // ResultsCacheConfig is the config for the results cache.
 type ResultsCacheConfig struct {
 	CacheConfig       cache.Config  `yaml:"cache"`
@@ -59,6 +64,7 @@ var PrometheusResponseExtractor = ExtractorFunc(func(start, end int64, from Resp
 			ResultType: promRes.Data.ResultType,
 			Result:     extractMatrix(start, end, promRes.Data.Result),
 		},
+		Headers: promRes.Headers,
 	}
 })
 
@@ -133,12 +139,41 @@ func (s resultsCache) Do(ctx context.Context, r Request) (Response, error) {
 	return response, err
 }
 
+// shouldCacheResponse says whether the response should be cached or not.
+func shouldCacheResponse(r Response) bool {
+	if promResp, ok := r.(*PrometheusResponse); ok {
+		shouldCache := true
+	outer:
+		for _, hv := range promResp.Headers {
+			if hv == nil {
+				continue
+			}
+			if hv.Name != cachecontrolHeader {
+				continue
+			}
+			for _, v := range hv.Values {
+				if v == noCacheValue {
+					shouldCache = false
+					break outer
+				}
+			}
+		}
+		return shouldCache
+	}
+	return true
+}
+
 func (s resultsCache) handleMiss(ctx context.Context, r Request) (Response, []Extent, error) {
 	response, err := s.next.Do(ctx, r)
 	if err != nil {
 		return nil, nil, err
 	}
 
+	if !shouldCacheResponse(response) {
+		level.Debug(s.logger).Log("msg", fmt.Sprintf("%s header in response is equal to %s, not caching the response", cachecontrolHeader, noCacheValue))
+		return response, []Extent{}, nil
+	}
+
 	extent, err := toExtent(ctx, r, response)
 	if err != nil {
 		return nil, nil, err

pkg/querier/queryrange/results_cache_test.go

@@ -31,6 +31,12 @@ var (
 		Step:  120 * 1e3,
 		Query: "sum(container_memory_rss) by (namespace)",
 	}
+	respHeaders = []*PrometheusResponseHeader{
+		{
+			Name:   "Content-Type",
+			Values: []string{"application/json"},
+		},
+	}
 	parsedResponse = &PrometheusResponse{
 		Status: "success",
 		Data: PrometheusData{
@@ -108,6 +114,57 @@ func mkExtent(start, end int64) Extent {
 	}
 }
 
+func TestShouldCache(t *testing.T) {
+	for i, tc := range []struct {
+		input    Response
+		expected bool
+	}{
+		// Does not contain the needed header.
+		{
+			input: Response(&PrometheusResponse{
+				Headers: []*PrometheusResponseHeader{
+					{
+						Name:   "meaninglessheader",
+						Values: []string{},
+					},
+				},
+			}),
+			expected: true,
+		},
+		// Does contain the header which has the value.
+		{
+			input: Response(&PrometheusResponse{
+				Headers: []*PrometheusResponseHeader{
+					{
+						Name:   cachecontrolHeader,
+						Values: []string{noCacheValue},
+					},
+				},
+			}),
+			expected: false,
+		},
+		// Header contains extra values but still good.
+		{
+			input: Response(&PrometheusResponse{
+				Headers: []*PrometheusResponseHeader{
+					{
+						Name:   cachecontrolHeader,
+						Values: []string{"foo", noCacheValue},
+					},
+				},
+			}),
+			expected: false,
+		},
+	} {
+		{
+			t.Run(strconv.Itoa(i), func(t *testing.T) {
+				ret := shouldCacheResponse(tc.input)
+				require.Equal(t, tc.expected, ret)
+			})
+		}
+	}
+}
+
 func TestPartiton(t *testing.T) {
 	for i, tc := range []struct {
 		input                  Request