diff --git a/.circleci/config.yml b/.circleci/config.yml
index e6638fc452..e8669fa87d 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -39,6 +39,7 @@ jobs:
           # don't limit this to the number of allocated cores, the job is
           # likely to get OOMed and killed.
           GOOPTS: "-p 2"
+          GOMAXPROCS: "2"
     - prometheus/check_proto
     - prometheus/store_artifact:
         file: prometheus
diff --git a/cmd/prometheus/query_log_test.go b/cmd/prometheus/query_log_test.go
new file mode 100644
index 0000000000..72629bcf36
--- /dev/null
+++ b/cmd/prometheus/query_log_test.go
@@ -0,0 +1,384 @@
+// Copyright 2020 The Prometheus 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 main
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/prometheus/prometheus/util/testutil"
+)
+
+type origin int
+
+const (
+	apiOrigin origin = iota
+	consoleOrigin
+	ruleOrigin
+)
+
+// queryLogTest defines a query log test.
+type queryLogTest struct {
+	origin         origin   // Kind of queries tested: api, console, rules.
+	prefix         string   // Set as --web.route-prefix.
+	host           string   // Used in --web.listen-address. Used with 127.0.0.1 and ::1.
+	port           int      // Used in --web.listen-address.
+	cwd            string   // Directory where the test is running. Required to find the rules in testdata.
+	configFile     *os.File // The configuration file.
+	enabledAtStart bool     // Whether query log is enabled at startup.
+}
+
+// skip checks if the test is needed and the prerequisites are met.
+func (p *queryLogTest) skip(t *testing.T) {
+	if p.prefix != "" && p.origin == ruleOrigin {
+		t.Skip("changing prefix has no effect on rules")
+	}
+	// Some systems don't support IPv4 or IPv6.
+	l, err := net.Listen("tcp", fmt.Sprintf("%s:0", p.host))
+	if err != nil {
+		t.Skip("ip version not supported")
+	}
+	l.Close()
+}
+
+// waitForPrometheus waits for Prometheus to be ready.
+func (p *queryLogTest) waitForPrometheus() error {
+	var err error
+	for x := 0; x < 20; x++ {
+		var r *http.Response
+		if r, err = http.Get(fmt.Sprintf("http://%s:%d%s/-/ready", p.host, p.port, p.prefix)); err == nil && r.StatusCode == 200 {
+			break
+		}
+		time.Sleep(500 * time.Millisecond)
+	}
+	return err
+}
+
+// setQueryLog alters the configuration file to enable or disable the query log,
+// then reloads the configuration if needed.
+func (p *queryLogTest) setQueryLog(t *testing.T, queryLogFile string) {
+	err := p.configFile.Truncate(0)
+	testutil.Ok(t, err)
+	_, err = p.configFile.Seek(0, 0)
+	testutil.Ok(t, err)
+	if queryLogFile != "" {
+		_, err = p.configFile.Write([]byte(fmt.Sprintf("global:\n  query_log_file: %s\n", queryLogFile)))
+		testutil.Ok(t, err)
+	}
+	_, err = p.configFile.Write([]byte(p.configuration()))
+	testutil.Ok(t, err)
+}
+
+// reloadConfig reloads the configuration using POST.
+func (p *queryLogTest) reloadConfig(t *testing.T) {
+	r, err := http.Post(fmt.Sprintf("http://%s:%d%s/-/reload", p.host, p.port, p.prefix), "text/plain", nil)
+	testutil.Ok(t, err)
+	testutil.Equals(t, 200, r.StatusCode)
+}
+
+// query runs a query according to the test origin.
+func (p *queryLogTest) query(t *testing.T) {
+	switch p.origin {
+	case apiOrigin:
+		r, err := http.Get(fmt.Sprintf(
+			"http://%s:%d%s/api/v1/query?query=%s",
+			p.host,
+			p.port,
+			p.prefix,
+			url.QueryEscape("query_with_api"),
+		))
+		testutil.Ok(t, err)
+		testutil.Equals(t, 200, r.StatusCode)
+	case consoleOrigin:
+		r, err := http.Get(fmt.Sprintf(
+			"http://%s:%d%s/consoles/test.html",
+			p.host,
+			p.port,
+			p.prefix,
+		))
+		testutil.Ok(t, err)
+		testutil.Equals(t, 200, r.StatusCode)
+	case ruleOrigin:
+		time.Sleep(2 * time.Second)
+	default:
+		panic("can't query this origin")
+	}
+}
+
+// queryString returns the expected queryString of a this test.
+func (p *queryLogTest) queryString() string {
+	switch p.origin {
+	case apiOrigin:
+		return "query_with_api"
+	case ruleOrigin:
+		return "query_in_rule"
+	case consoleOrigin:
+		return "query_in_console"
+	default:
+		panic("unknown origin")
+	}
+}
+
+// validateLastQuery checks that the last query in the query log matches the
+// test parameters.
+func (p *queryLogTest) validateLastQuery(t *testing.T, ql []queryLogLine) {
+	q := ql[len(ql)-1]
+	testutil.Equals(t, q["query"].(string), p.queryString())
+	switch p.origin {
+	case consoleOrigin:
+		testutil.Equals(t, q["path"].(string), p.prefix+"/consoles/test.html")
+	case apiOrigin:
+		testutil.Equals(t, q["path"].(string), p.prefix+"/api/v1/query")
+	case ruleOrigin:
+		testutil.Equals(t, q["groupName"].(string), "querylogtest")
+		testutil.Equals(t, q["groupFile"].(string), filepath.Join(p.cwd, "testdata", "rules", "test.yml"))
+	default:
+		panic("unknown origin")
+	}
+	if p.origin != ruleOrigin {
+		host := p.host
+		if host == "[::1]" {
+			host = "::1"
+		}
+		testutil.Equals(t, q["clientIP"].(string), host)
+	}
+}
+
+func (p *queryLogTest) String() string {
+	var name string
+	switch p.origin {
+	case apiOrigin:
+		name = "api queries"
+	case consoleOrigin:
+		name = "console queries"
+	case ruleOrigin:
+		name = "rule queries"
+	}
+	name = name + ", " + p.host + ":" + strconv.Itoa(p.port)
+	if p.enabledAtStart {
+		name = name + ", enabled at start"
+	}
+	if p.prefix != "" {
+		name = name + ", with prefix " + p.prefix
+	}
+	return name
+}
+
+// params returns the specific command line parameters of this test.
+func (p *queryLogTest) params() []string {
+	s := []string{}
+	if p.prefix != "" {
+		s = append(s, "--web.route-prefix="+p.prefix)
+	}
+	if p.origin == consoleOrigin {
+		s = append(s, "--web.console.templates="+filepath.Join("testdata", "consoles"))
+	}
+	return s
+}
+
+// configuration returns the specific configuration lines required for this
+// test.
+func (p *queryLogTest) configuration() string {
+	switch p.origin {
+	case ruleOrigin:
+		return "\nrule_files:\n- " + filepath.Join(p.cwd, "testdata", "rules", "test.yml") + "\n"
+	default:
+		return "\n"
+	}
+}
+
+// exactQueryCount returns wheter we can match an exact query count. False on
+// recording rules are they are regular time intervals.
+func (p *queryLogTest) exactQueryCount() bool {
+	return p.origin != ruleOrigin
+}
+
+// run launches the scenario of this query log test.
+func (p *queryLogTest) run(t *testing.T) {
+	p.skip(t)
+
+	// Setup temporary files for this test.
+	queryLogFile, err := ioutil.TempFile("", "query")
+	testutil.Ok(t, err)
+	defer os.Remove(queryLogFile.Name())
+	p.configFile, err = ioutil.TempFile("", "config")
+	testutil.Ok(t, err)
+	defer os.Remove(p.configFile.Name())
+
+	if p.enabledAtStart {
+		p.setQueryLog(t, queryLogFile.Name())
+	} else {
+		p.setQueryLog(t, "")
+	}
+
+	params := append([]string{"-test.main", "--config.file=" + p.configFile.Name(), "--web.enable-lifecycle", fmt.Sprintf("--web.listen-address=%s:%d", p.host, p.port)}, p.params()...)
+
+	prom := exec.Command(promPath, params...)
+
+	// Log stderr in case of failure.
+	stderr, err := prom.StderrPipe()
+	testutil.Ok(t, err)
+	go func() {
+		slurp, _ := ioutil.ReadAll(stderr)
+		t.Log(string(slurp))
+	}()
+
+	testutil.Ok(t, prom.Start())
+
+	defer func() {
+		prom.Process.Signal(os.Interrupt)
+		prom.Wait()
+	}()
+	testutil.Ok(t, p.waitForPrometheus())
+
+	if !p.enabledAtStart {
+		p.query(t)
+		testutil.Equals(t, 0, len(readQueryLog(t, queryLogFile.Name())))
+		p.setQueryLog(t, queryLogFile.Name())
+		p.reloadConfig(t)
+	}
+
+	p.query(t)
+
+	ql := readQueryLog(t, queryLogFile.Name())
+	qc := len(ql)
+	if p.exactQueryCount() {
+		testutil.Equals(t, 1, qc)
+	} else {
+		testutil.Assert(t, qc > 0, "no queries logged")
+	}
+	p.validateLastQuery(t, ql)
+
+	p.setQueryLog(t, "")
+	p.reloadConfig(t)
+	if !p.exactQueryCount() {
+		qc = len(readQueryLog(t, queryLogFile.Name()))
+	}
+
+	p.query(t)
+
+	ql = readQueryLog(t, queryLogFile.Name())
+	testutil.Equals(t, qc, len(ql))
+
+	qc = len(ql)
+	p.setQueryLog(t, queryLogFile.Name())
+	p.reloadConfig(t)
+
+	p.query(t)
+	qc++
+
+	ql = readQueryLog(t, queryLogFile.Name())
+	if p.exactQueryCount() {
+		testutil.Equals(t, qc, len(ql))
+	} else {
+		testutil.Assert(t, len(ql) > qc, "no queries logged")
+	}
+	p.validateLastQuery(t, ql)
+	qc = len(ql)
+
+	// Move the file, Prometheus should still write to the old file.
+	newFile, err := ioutil.TempFile("", "newLoc")
+	testutil.Ok(t, err)
+	defer os.Remove(newFile.Name())
+	testutil.Ok(t, os.Rename(queryLogFile.Name(), newFile.Name()))
+	ql = readQueryLog(t, newFile.Name())
+	if p.exactQueryCount() {
+		testutil.Equals(t, qc, len(ql))
+	}
+	p.validateLastQuery(t, ql)
+	qc = len(ql)
+
+	p.query(t)
+
+	qc++
+
+	ql = readQueryLog(t, newFile.Name())
+	if p.exactQueryCount() {
+		testutil.Equals(t, qc, len(ql))
+	} else {
+		testutil.Assert(t, len(ql) > qc, "no queries logged")
+	}
+	p.validateLastQuery(t, ql)
+
+	p.reloadConfig(t)
+
+	p.query(t)
+
+	ql = readQueryLog(t, queryLogFile.Name())
+	qc = len(ql)
+	if p.exactQueryCount() {
+		testutil.Equals(t, 1, qc)
+	} else {
+		testutil.Assert(t, qc > 0, "no queries logged")
+	}
+}
+
+type queryLogLine map[string]interface{}
+
+// readQueryLog unmarshal a json-formatted query log into query log lines.
+func readQueryLog(t *testing.T, path string) []queryLogLine {
+	ql := []queryLogLine{}
+	file, err := os.Open(path)
+	testutil.Ok(t, err)
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		var q queryLogLine
+		testutil.Ok(t, json.Unmarshal(scanner.Bytes(), &q))
+		ql = append(ql, q)
+	}
+	return ql
+}
+
+func TestQueryLog(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode.")
+	}
+
+	cwd, err := os.Getwd()
+	testutil.Ok(t, err)
+
+	port := 15000
+	for _, host := range []string{"127.0.0.1", "[::1]"} {
+		for _, prefix := range []string{"", "/foobar"} {
+			for _, enabledAtStart := range []bool{true, false} {
+				for _, origin := range []origin{apiOrigin, consoleOrigin, ruleOrigin} {
+					p := &queryLogTest{
+						origin:         origin,
+						host:           host,
+						enabledAtStart: enabledAtStart,
+						prefix:         prefix,
+						port:           port,
+						cwd:            cwd,
+					}
+
+					t.Run(p.String(), func(t *testing.T) {
+						p.run(t)
+					})
+				}
+			}
+		}
+	}
+}
diff --git a/cmd/prometheus/testdata/consoles/test.html b/cmd/prometheus/testdata/consoles/test.html
new file mode 100644
index 0000000000..c3ff96da11
--- /dev/null
+++ b/cmd/prometheus/testdata/consoles/test.html
@@ -0,0 +1 @@
+{{ query "query_in_console" }}
diff --git a/cmd/prometheus/testdata/rules/test.yml b/cmd/prometheus/testdata/rules/test.yml
new file mode 100644
index 0000000000..91ee987b85
--- /dev/null
+++ b/cmd/prometheus/testdata/rules/test.yml
@@ -0,0 +1,6 @@
+groups:
+  - name: querylogtest
+    interval: 1s
+    rules:
+      - record: test
+        expr: query_in_rule