prometheus/discovery/marathon/marathon.go
beorn7 5b53aa1108 style: Replace else if cascades with switch
Wiser coders than myself have come to the conclusion that a `switch`
statement is almost always superior to a statement that includes any
`else if`.

The exceptions that I have found in our codebase are just these two:

* The `if else` is followed by an additional statement before the next
  condition (separated by a `;`).
* The whole thing is within a `for` loop and `break` statements are
  used. In this case, using `switch` would require tagging the `for`
  loop, which probably tips the balance.

Why are `switch` statements more readable?

For one, fewer curly braces. But more importantly, the conditions all
have the same alignment, so the whole thing follows the natural flow
of going down a list of conditions. With `else if`, in contrast, all
conditions but the first are "hidden" behind `} else if `, harder to
spot and (for no good reason) presented differently from the first
condition.

I'm sure the aforemention wise coders can list even more reasons.

In any case, I like it so much that I have found myself recommending
it in code reviews. I would like to make it a habit in our code base,
without making it a hard requirement that we would test on the CI. But
for that, there has to be a role model, so this commit eliminates all
`if else` occurrences, unless it is autogenerated code or fits one of
the exceptions above.

Signed-off-by: beorn7 <beorn@grafana.com>
2023-04-19 17:22:31 +02:00

517 lines
17 KiB
Go

// Copyright 2016 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 marathon
import (
"context"
"encoding/json"
"errors"
"fmt"
"io"
"math/rand"
"net"
"net/http"
"os"
"strconv"
"strings"
"time"
"github.com/go-kit/log"
"github.com/prometheus/common/config"
"github.com/prometheus/common/model"
"github.com/prometheus/prometheus/discovery"
"github.com/prometheus/prometheus/discovery/refresh"
"github.com/prometheus/prometheus/discovery/targetgroup"
"github.com/prometheus/prometheus/util/strutil"
)
const (
// metaLabelPrefix is the meta prefix used for all meta labels in this discovery.
metaLabelPrefix = model.MetaLabelPrefix + "marathon_"
// appLabelPrefix is the prefix for the application labels.
appLabelPrefix = metaLabelPrefix + "app_label_"
// appLabel is used for the name of the app in Marathon.
appLabel model.LabelName = metaLabelPrefix + "app"
// imageLabel is the label that is used for the docker image running the service.
imageLabel model.LabelName = metaLabelPrefix + "image"
// portIndexLabel is the integer port index when multiple ports are defined;
// e.g. PORT1 would have a value of '1'
portIndexLabel model.LabelName = metaLabelPrefix + "port_index"
// taskLabel contains the mesos task name of the app instance.
taskLabel model.LabelName = metaLabelPrefix + "task"
// portMappingLabelPrefix is the prefix for the application portMappings labels.
portMappingLabelPrefix = metaLabelPrefix + "port_mapping_label_"
// portDefinitionLabelPrefix is the prefix for the application portDefinitions labels.
portDefinitionLabelPrefix = metaLabelPrefix + "port_definition_label_"
)
// DefaultSDConfig is the default Marathon SD configuration.
var DefaultSDConfig = SDConfig{
RefreshInterval: model.Duration(30 * time.Second),
HTTPClientConfig: config.DefaultHTTPClientConfig,
}
func init() {
discovery.RegisterConfig(&SDConfig{})
}
// SDConfig is the configuration for services running on Marathon.
type SDConfig struct {
Servers []string `yaml:"servers,omitempty"`
RefreshInterval model.Duration `yaml:"refresh_interval,omitempty"`
AuthToken config.Secret `yaml:"auth_token,omitempty"`
AuthTokenFile string `yaml:"auth_token_file,omitempty"`
HTTPClientConfig config.HTTPClientConfig `yaml:",inline"`
}
// Name returns the name of the Config.
func (*SDConfig) Name() string { return "marathon" }
// NewDiscoverer returns a Discoverer for the Config.
func (c *SDConfig) NewDiscoverer(opts discovery.DiscovererOptions) (discovery.Discoverer, error) {
return NewDiscovery(*c, opts.Logger)
}
// SetDirectory joins any relative file paths with dir.
func (c *SDConfig) SetDirectory(dir string) {
c.HTTPClientConfig.SetDirectory(dir)
c.AuthTokenFile = config.JoinDir(dir, c.AuthTokenFile)
}
// UnmarshalYAML implements the yaml.Unmarshaler interface.
func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
*c = DefaultSDConfig
type plain SDConfig
err := unmarshal((*plain)(c))
if err != nil {
return err
}
if len(c.Servers) == 0 {
return errors.New("marathon_sd: must contain at least one Marathon server")
}
if len(c.AuthToken) > 0 && len(c.AuthTokenFile) > 0 {
return errors.New("marathon_sd: at most one of auth_token & auth_token_file must be configured")
}
if c.HTTPClientConfig.BasicAuth != nil && (len(c.AuthToken) > 0 || len(c.AuthTokenFile) > 0) {
return errors.New("marathon_sd: at most one of basic_auth, auth_token & auth_token_file must be configured")
}
if (len(c.HTTPClientConfig.BearerToken) > 0 || len(c.HTTPClientConfig.BearerTokenFile) > 0) && (len(c.AuthToken) > 0 || len(c.AuthTokenFile) > 0) {
return errors.New("marathon_sd: at most one of bearer_token, bearer_token_file, auth_token & auth_token_file must be configured")
}
if c.HTTPClientConfig.Authorization != nil && (len(c.AuthToken) > 0 || len(c.AuthTokenFile) > 0) {
return errors.New("marathon_sd: at most one of auth_token, auth_token_file & authorization must be configured")
}
return c.HTTPClientConfig.Validate()
}
const appListPath string = "/v2/apps/?embed=apps.tasks"
// Discovery provides service discovery based on a Marathon instance.
type Discovery struct {
*refresh.Discovery
client *http.Client
servers []string
lastRefresh map[string]*targetgroup.Group
appsClient appListClient
}
// NewDiscovery returns a new Marathon Discovery.
func NewDiscovery(conf SDConfig, logger log.Logger) (*Discovery, error) {
rt, err := config.NewRoundTripperFromConfig(conf.HTTPClientConfig, "marathon_sd")
if err != nil {
return nil, err
}
switch {
case len(conf.AuthToken) > 0:
rt, err = newAuthTokenRoundTripper(conf.AuthToken, rt)
case len(conf.AuthTokenFile) > 0:
rt, err = newAuthTokenFileRoundTripper(conf.AuthTokenFile, rt)
}
if err != nil {
return nil, err
}
d := &Discovery{
client: &http.Client{Transport: rt},
servers: conf.Servers,
appsClient: fetchApps,
}
d.Discovery = refresh.NewDiscovery(
logger,
"marathon",
time.Duration(conf.RefreshInterval),
d.refresh,
)
return d, nil
}
type authTokenRoundTripper struct {
authToken config.Secret
rt http.RoundTripper
}
// newAuthTokenRoundTripper adds the provided auth token to a request.
func newAuthTokenRoundTripper(token config.Secret, rt http.RoundTripper) (http.RoundTripper, error) {
return &authTokenRoundTripper{token, rt}, nil
}
func (rt *authTokenRoundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
// According to https://docs.mesosphere.com/1.11/security/oss/managing-authentication/
// DC/OS wants with "token=" a different Authorization header than implemented in httputil/client.go
// so we set this explicitly here.
request.Header.Set("Authorization", "token="+string(rt.authToken))
return rt.rt.RoundTrip(request)
}
type authTokenFileRoundTripper struct {
authTokenFile string
rt http.RoundTripper
}
// newAuthTokenFileRoundTripper adds the auth token read from the file to a request.
func newAuthTokenFileRoundTripper(tokenFile string, rt http.RoundTripper) (http.RoundTripper, error) {
// fail-fast if we can't read the file.
_, err := os.ReadFile(tokenFile)
if err != nil {
return nil, fmt.Errorf("unable to read auth token file %s: %w", tokenFile, err)
}
return &authTokenFileRoundTripper{tokenFile, rt}, nil
}
func (rt *authTokenFileRoundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
b, err := os.ReadFile(rt.authTokenFile)
if err != nil {
return nil, fmt.Errorf("unable to read auth token file %s: %w", rt.authTokenFile, err)
}
authToken := strings.TrimSpace(string(b))
// According to https://docs.mesosphere.com/1.11/security/oss/managing-authentication/
// DC/OS wants with "token=" a different Authorization header than implemented in httputil/client.go
// so we set this explicitly here.
request.Header.Set("Authorization", "token="+authToken)
return rt.rt.RoundTrip(request)
}
func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
targetMap, err := d.fetchTargetGroups(ctx)
if err != nil {
return nil, err
}
all := make([]*targetgroup.Group, 0, len(targetMap))
for _, tg := range targetMap {
all = append(all, tg)
}
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
}
// Remove services which did disappear.
for source := range d.lastRefresh {
_, ok := targetMap[source]
if !ok {
all = append(all, &targetgroup.Group{Source: source})
}
}
d.lastRefresh = targetMap
return all, nil
}
func (d *Discovery) fetchTargetGroups(ctx context.Context) (map[string]*targetgroup.Group, error) {
url := randomAppsURL(d.servers)
apps, err := d.appsClient(ctx, d.client, url)
if err != nil {
return nil, err
}
groups := appsToTargetGroups(apps)
return groups, nil
}
// task describes one instance of a service running on Marathon.
type task struct {
ID string `json:"id"`
Host string `json:"host"`
Ports []uint32 `json:"ports"`
IPAddresses []ipAddress `json:"ipAddresses"`
}
// ipAddress describes the address and protocol the container's network interface is bound to.
type ipAddress struct {
Address string `json:"ipAddress"`
Proto string `json:"protocol"`
}
// PortMapping describes in which port the process are binding inside the docker container.
type portMapping struct {
Labels map[string]string `json:"labels"`
ContainerPort uint32 `json:"containerPort"`
HostPort uint32 `json:"hostPort"`
ServicePort uint32 `json:"servicePort"`
}
// DockerContainer describes a container which uses the docker runtime.
type dockerContainer struct {
Image string `json:"image"`
PortMappings []portMapping `json:"portMappings"`
}
// Container describes the runtime an app in running in.
type container struct {
Docker dockerContainer `json:"docker"`
PortMappings []portMapping `json:"portMappings"`
}
// PortDefinition describes which load balancer port you should access to access the service.
type portDefinition struct {
Labels map[string]string `json:"labels"`
Port uint32 `json:"port"`
}
// Network describes the name and type of network the container is attached to.
type network struct {
Name string `json:"name"`
Mode string `json:"mode"`
}
// App describes a service running on Marathon.
type app struct {
ID string `json:"id"`
Tasks []task `json:"tasks"`
RunningTasks int `json:"tasksRunning"`
Labels map[string]string `json:"labels"`
Container container `json:"container"`
PortDefinitions []portDefinition `json:"portDefinitions"`
Networks []network `json:"networks"`
RequirePorts bool `json:"requirePorts"`
}
// isContainerNet checks if the app's first network is set to mode 'container'.
func (app app) isContainerNet() bool {
return len(app.Networks) > 0 && app.Networks[0].Mode == "container"
}
// appList is a list of Marathon apps.
type appList struct {
Apps []app `json:"apps"`
}
// appListClient defines a function that can be used to get an application list from marathon.
type appListClient func(ctx context.Context, client *http.Client, url string) (*appList, error)
// fetchApps requests a list of applications from a marathon server.
func fetchApps(ctx context.Context, client *http.Client, url string) (*appList, error) {
request, err := http.NewRequest("GET", url, nil)
if err != nil {
return nil, err
}
request = request.WithContext(ctx)
resp, err := client.Do(request)
if err != nil {
return nil, err
}
defer func() {
io.Copy(io.Discard, resp.Body)
resp.Body.Close()
}()
if (resp.StatusCode < 200) || (resp.StatusCode >= 300) {
return nil, fmt.Errorf("non 2xx status '%v' response during marathon service discovery", resp.StatusCode)
}
b, err := io.ReadAll(resp.Body)
if err != nil {
return nil, err
}
var apps appList
err = json.Unmarshal(b, &apps)
if err != nil {
return nil, fmt.Errorf("%q: %w", url, err)
}
return &apps, nil
}
// randomAppsURL randomly selects a server from an array and creates
// an URL pointing to the app list.
func randomAppsURL(servers []string) string {
// TODO: If possible update server list from Marathon at some point.
server := servers[rand.Intn(len(servers))]
return fmt.Sprintf("%s%s", server, appListPath)
}
// appsToTargetGroups takes an array of Marathon apps and converts them into target groups.
func appsToTargetGroups(apps *appList) map[string]*targetgroup.Group {
tgroups := map[string]*targetgroup.Group{}
for _, a := range apps.Apps {
group := createTargetGroup(&a)
tgroups[group.Source] = group
}
return tgroups
}
func createTargetGroup(app *app) *targetgroup.Group {
var (
targets = targetsForApp(app)
appName = model.LabelValue(app.ID)
image = model.LabelValue(app.Container.Docker.Image)
)
tg := &targetgroup.Group{
Targets: targets,
Labels: model.LabelSet{
appLabel: appName,
imageLabel: image,
},
Source: app.ID,
}
for ln, lv := range app.Labels {
ln = appLabelPrefix + strutil.SanitizeLabelName(ln)
tg.Labels[model.LabelName(ln)] = model.LabelValue(lv)
}
return tg
}
func targetsForApp(app *app) []model.LabelSet {
targets := make([]model.LabelSet, 0, len(app.Tasks))
var ports []uint32
var labels []map[string]string
var prefix string
switch {
case len(app.Container.PortMappings) != 0:
// In Marathon 1.5.x the "container.docker.portMappings" object was moved
// to "container.portMappings".
ports, labels = extractPortMapping(app.Container.PortMappings, app.isContainerNet())
prefix = portMappingLabelPrefix
case len(app.Container.Docker.PortMappings) != 0:
// Prior to Marathon 1.5 the port mappings could be found at the path
// "container.docker.portMappings".
ports, labels = extractPortMapping(app.Container.Docker.PortMappings, app.isContainerNet())
prefix = portMappingLabelPrefix
case len(app.PortDefinitions) != 0:
// PortDefinitions deprecates the "ports" array and can be used to specify
// a list of ports with metadata in case a mapping is not required.
ports = make([]uint32, len(app.PortDefinitions))
labels = make([]map[string]string, len(app.PortDefinitions))
for i := 0; i < len(app.PortDefinitions); i++ {
labels[i] = app.PortDefinitions[i].Labels
// When requirePorts is false, this port becomes the 'servicePort', not the listen port.
// In this case, the port needs to be taken from the task instead of the app.
if app.RequirePorts {
ports[i] = app.PortDefinitions[i].Port
}
}
prefix = portDefinitionLabelPrefix
}
// Gather info about the app's 'tasks'. Each instance (container) is considered a task
// and can be reachable at one or more host:port endpoints.
for _, t := range app.Tasks {
// There are no labels to gather if only Ports is defined. (eg. with host networking)
// Ports can only be gathered from the Task (not from the app) and are guaranteed
// to be the same across all tasks. If we haven't gathered any ports by now,
// use the task's ports as the port list.
if len(ports) == 0 && len(t.Ports) != 0 {
ports = t.Ports
}
// Iterate over the ports we gathered using one of the methods above.
for i, port := range ports {
// A zero port here means that either the portMapping has a zero port defined,
// or there is a portDefinition with requirePorts set to false. This means the port
// is auto-generated by Mesos and needs to be looked up in the task.
if port == 0 && len(t.Ports) == len(ports) {
port = t.Ports[i]
}
// Each port represents a possible Prometheus target.
targetAddress := targetEndpoint(&t, port, app.isContainerNet())
target := model.LabelSet{
model.AddressLabel: model.LabelValue(targetAddress),
taskLabel: model.LabelValue(t.ID),
portIndexLabel: model.LabelValue(strconv.Itoa(i)),
}
// Gather all port labels and set them on the current target, skip if the port has no Marathon labels.
// This will happen in the host networking case with only `ports` defined, where
// it is inefficient to allocate a list of possibly hundreds of empty label maps per host port.
if len(labels) > 0 {
for ln, lv := range labels[i] {
ln = prefix + strutil.SanitizeLabelName(ln)
target[model.LabelName(ln)] = model.LabelValue(lv)
}
}
targets = append(targets, target)
}
}
return targets
}
// Generate a target endpoint string in host:port format.
func targetEndpoint(task *task, port uint32, containerNet bool) string {
var host string
// Use the task's ipAddress field when it's in a container network
if containerNet && len(task.IPAddresses) > 0 {
host = task.IPAddresses[0].Address
} else {
host = task.Host
}
return net.JoinHostPort(host, fmt.Sprintf("%d", port))
}
// Get a list of ports and a list of labels from a PortMapping.
func extractPortMapping(portMappings []portMapping, containerNet bool) ([]uint32, []map[string]string) {
ports := make([]uint32, len(portMappings))
labels := make([]map[string]string, len(portMappings))
for i := 0; i < len(portMappings); i++ {
labels[i] = portMappings[i].Labels
if containerNet {
// If the app is in a container network, connect directly to the container port.
ports[i] = portMappings[i].ContainerPort
} else {
// Otherwise, connect to the allocated host port for the container.
// Note that this host port is likely set to 0 in the app definition, which means it is
// automatically generated and needs to be extracted from the task's 'ports' array at a later stage.
ports[i] = portMappings[i].HostPort
}
}
return ports, labels
}