From 68d4423c3c6aeec2c8bb1c058aa26122f1301835 Mon Sep 17 00:00:00 2001
From: James Munnelly <james@munnelly.eu>
Date: Mon, 18 Sep 2017 11:59:28 +0100
Subject: [PATCH 1/2] Add support for optional jitter parameter on CN

---
 vault_resource.go   | 7 +++++++
 vault_resources.go  | 6 ++++++
 watched_resource.go | 7 +++++++
 3 files changed, 20 insertions(+)

diff --git a/vault_resource.go b/vault_resource.go
index 82b1fcc..8ad2fa6 100644
--- a/vault_resource.go
+++ b/vault_resource.go
@@ -48,6 +48,10 @@ const (
 	optionMode = "mode"
 	// optionMaxRetries is the maximum number of retries that should be attempted
 	optionMaxRetries = "retries"
+	// optionMaxJitter is the maximum amount of jitter that should be applied
+	// to updates for this resource. If non-zero, a random value between 0 and
+	// maxJitter will be subtracted from the update period.
+	optionMaxJitter = "jitter"
 	// defaultSize sets the default size of a generic secret
 	defaultSize = 20
 )
@@ -117,6 +121,9 @@ type VaultResource struct {
 	// retries is the number of times this resource has been retried since it
 	// last succeeded
 	retries int
+	// maxJitter is the maximum jitter duration to use for this resource when
+	// performing renewals
+	maxJitter time.Duration
 }
 
 // GetFilename generates a resource filename by default the resource name and resource type, which
diff --git a/vault_resources.go b/vault_resources.go
index ac6f1ce..36ffaf2 100644
--- a/vault_resources.go
+++ b/vault_resources.go
@@ -137,6 +137,12 @@ func (r *VaultResources) Set(value string) error {
 					return fmt.Errorf("the retries option: %s is invalid, should be an integer", value)
 				}
 				rn.maxRetries = int(maxRetries)
+			case optionMaxJitter:
+				maxJitter, err := time.ParseDuration(value)
+				if err != nil {
+					return fmt.Errorf("the jitter option: %s is invalid, should be in duration format", value)
+				}
+				rn.maxJitter = maxJitter
 			default:
 				rn.options[name] = value
 			}
diff --git a/watched_resource.go b/watched_resource.go
index 3e57e2d..8e21d6c 100644
--- a/watched_resource.go
+++ b/watched_resource.go
@@ -57,6 +57,13 @@ func (r *watchedResource) notifyOnRenewal(ch chan *watchedResource) {
 			}
 			r.renewalTime = r.calculateRenewal()
 		}
+		if r.resource.maxJitter != 0 {
+			glog.V(4).Infof("using maxJitter (%s) to calculate renewal time", r.resource.maxJitter)
+			r.renewalTime = time.Duration(getDurationWithin(
+				int((r.renewalTime-r.resource.maxJitter)/time.Second),
+				int(r.renewalTime/time.Second),
+			))
+		}
 		glog.V(3).Infof("setting a renewal notification on resource: %s, time: %s", r.resource, r.renewalTime)
 		// step: wait for the duration
 		<-time.After(r.renewalTime)

From 17ff26ba79b7e8afd6cb3d51ce8020fa0575279d Mon Sep 17 00:00:00 2001
From: James Munnelly <james@munnelly.eu>
Date: Mon, 18 Sep 2017 12:02:59 +0100
Subject: [PATCH 2/2] Add entry in README.md

---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index c5d3ead..638f479 100644
--- a/README.md
+++ b/README.md
@@ -147,3 +147,4 @@ bundle format is very similar in the sense it similar takes the private key and
 - **fmt**: (format) allows you to specify the output format of the resource / secret, e.g json, yaml, ini, txt
 - **exec** (execute) execute's a command when resource is updated or changed
 - **retries**: (retries) the maximum number of times to retry retrieving a resource. If not set, resources will be retried indefinitely
+* **jitter**: (jitter) an optional maximum jitter duration. If specified, a random duration between 0 and `jitter` will be subtracted from the renewal time for the resource