[amtool] - Add new command to update silence (#1123)

This adds a new command, update (and also its alias, extend), to update
existing silence in Alertmanager. User can use this command to update the
expiration or comment on existing silences. The API already support this
so I only expose the same functionality to amtool.

Don't allow update CreatedBy field as it is "Created" not "Updated", so
we should keep the original author.

cli/silence.go

@@ -32,4 +32,5 @@ func init() {
 	silenceCmd.AddCommand(expireCmd)
 	silenceCmd.AddCommand(queryCmd)
 	silenceCmd.AddCommand(importCmd)
+	silenceCmd.AddCommand(updateCmd)
 }

cli/silence_update.go

@@ -0,0 +1,147 @@
+package cli
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"path"
+	"time"
+
+	"github.com/prometheus/alertmanager/cli/format"
+	"github.com/prometheus/alertmanager/types"
+	"github.com/spf13/cobra"
+	flag "github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+type getResponse struct {
+	Status    string        `json:"status"`
+	Data      types.Silence `json:"data,omitempty"`
+	ErrorType string        `json:"errorType,omitempty"`
+	Error     string        `json:"error,omitempty"`
+}
+
+var updateFlags *flag.FlagSet
+var updateCmd = &cobra.Command{
+	Use:     "update <id> ...",
+	Aliases: []string{"extend"},
+	Args:    cobra.MinimumNArgs(1),
+	Short:   "Update silences",
+	Long:    `Extend or update existing silence in Alertmanager.`,
+	Run:     CommandWrapper(update),
+}
+
+func init() {
+	updateCmd.Flags().StringP("expires", "e", "", "Duration of silence (100h)")
+	updateCmd.Flags().String("expire-on", "", "Expire at a certain time (Overwrites expires) RFC3339 format 2006-01-02T15:04:05Z07:00")
+	updateCmd.Flags().StringP("comment", "c", "", "A comment to help describe the silence")
+	updateFlags = updateCmd.Flags()
+}
+
+func update(cmd *cobra.Command, args []string) error {
+	if len(args) < 1 {
+		return fmt.Errorf("no silence IDs specified")
+	}
+
+	alertmanagerUrl, err := GetAlertmanagerURL()
+	if err != nil {
+		return err
+	}
+
+	var updatedSilences []types.Silence
+	for _, silenceId := range args {
+		silence, err := getSilenceById(silenceId, *alertmanagerUrl)
+		if err != nil {
+			return err
+		}
+		silence, err = updateSilence(silence)
+		if err != nil {
+			return err
+		}
+		updatedSilences = append(updatedSilences, *silence)
+	}
+
+	quiet := viper.GetBool("quiet")
+	if quiet {
+		for _, silence := range updatedSilences {
+			fmt.Println(silence.ID)
+		}
+	} else {
+		formatter, found := format.Formatters[viper.GetString("output")]
+		if !found {
+			return fmt.Errorf("unknown output formatter")
+		}
+		formatter.FormatSilences(updatedSilences)
+	}
+	return nil
+}
+
+// This takes an url.URL and not a pointer as we will modify it for our API call.
+func getSilenceById(silenceId string, baseUrl url.URL) (*types.Silence, error) {
+	baseUrl.Path = path.Join(baseUrl.Path, "/api/v1/silence", silenceId)
+	res, err := http.Get(baseUrl.String())
+	if err != nil {
+		return nil, err
+	}
+
+	defer res.Body.Close()
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		return nil, fmt.Errorf("couldn't read response body: %v", err)
+	}
+
+	if res.StatusCode == 404 {
+		return nil, fmt.Errorf("no silence found with id: %v", silenceId)
+	}
+	if res.StatusCode != 200 {
+		return nil, fmt.Errorf("received %d response from Alertmanager: %v", res.StatusCode, body)
+	}
+
+	var response getResponse
+	err = json.Unmarshal(body, &response)
+	return &response.Data, nil
+}
+
+func updateSilence(silence *types.Silence) (*types.Silence, error) {
+	if updateFlags.Changed("expires") {
+		expires, err := updateFlags.GetString("expires")
+		if err != nil {
+			return nil, err
+		}
+		duration, err := time.ParseDuration(expires)
+		if err != nil {
+			return nil, err
+		}
+		silence.EndsAt = time.Now().UTC().Add(duration)
+	}
+
+	// expire-on will override expires value if both are specified
+	if updateFlags.Changed("expire-on") {
+		expireOn, err := updateFlags.GetString("expire-on")
+		if err != nil {
+			return nil, err
+		}
+		endsAt, err := time.Parse(time.RFC3339, expireOn)
+		if err != nil {
+			return nil, err
+		}
+		silence.EndsAt = endsAt
+	}
+
+	if updateFlags.Changed("comment") {
+		comment, err := updateFlags.GetString("comment")
+		if err != nil {
+			return nil, err
+		}
+		silence.Comment = comment
+	}
+
+	// addSilence can also be used to update an existing silence
+	_, err := addSilence(silence)
+	if err != nil {
+		return nil, err
+	}
+	return silence, nil
+}