fix: retry docker volume remove (!399)

Closes coop-cloud/organising#509

Reviewed-on: coop-cloud/abra#399
Reviewed-by: decentral1se <decentral1se@noreply.git.coopcloud.tech>
Co-authored-by: p4u1 <p4u1_f4u1@riseup.net>
Co-committed-by: p4u1 <p4u1_f4u1@riseup.net>

cli/app/remove.go

@@ -3,7 +3,9 @@ package app
 import (
 	"context"
 	"fmt"
+	"log"
 	"os"
+	"time"
 
 	"coopcloud.tech/abra/cli/internal"
 	"coopcloud.tech/abra/pkg/autocomplete"
@@ -124,9 +126,11 @@ flag.
 
 		if len(vols) > 0 {
 			for _, vol := range vols {
-				err := cl.VolumeRemove(context.Background(), vol, internal.Force) // last argument is for force removing
+				err = retryFunc(5, func() error {
+					return cl.VolumeRemove(context.Background(), vol, internal.Force) // last argument is for force removing
+				})
 				if err != nil {
-					logrus.Fatal(err)
+					log.Fatalf("removing volumes failed: %s", err)
 				}
 				logrus.Info(fmt.Sprintf("volume %s removed", vol))
 			}
@@ -143,3 +147,21 @@ flag.
 		return nil
 	},
 }
+
+// retryFunc retries the given function for the given retries. After the nth
+// retry it waits (n + 1)^2 seconds before the next retry (starting with n=0).
+// It returns an error if the function still failed after the last retry.
+func retryFunc(retries int, fn func() error) error {
+	for i := 0; i < retries; i++ {
+		err := fn()
+		if err == nil {
+			return nil
+		}
+		if i+1 < retries {
+			sleep := time.Duration(i+1) * time.Duration(i+1)
+			logrus.Infof("%s: waiting %d seconds before next retry", err, sleep)
+			time.Sleep(sleep * time.Second)
+		}
+	}
+	return fmt.Errorf("%d retries failed", retries)
+}