From d2be9d38dade36f35791962aa948382abb72b030 Mon Sep 17 00:00:00 2001
From: Pierre Souchay <p.souchay@criteo.com>
Date: Mon, 24 Aug 2020 23:33:10 +0200
Subject: [PATCH] Ensure that Cache options are reloaded when `consul reload`
 is performed.

This will apply cache throttling parameters are properly applied:
 * cache.EntryFetchMaxBurst
 * cache.EntryFetchRate

When values are updated, a log is displayed in info.
---
 agent/agent.go       |  6 ++++++
 agent/cache/cache.go | 33 ++++++++++++++++++++++++++++++---
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/agent/agent.go b/agent/agent.go
index bc676b0bfa..ab240e0af3 100644
--- a/agent/agent.go
+++ b/agent/agent.go
@@ -3748,6 +3748,12 @@ func (a *Agent) reloadConfigInternal(newCfg *config.RuntimeConfig) error {
 		return err
 	}
 
+	if a.cache.ReloadOptions(newCfg.Cache) {
+		a.logger.Info("Cache options have been updated")
+	} else {
+		a.logger.Debug("Cache options have not been modified")
+	}
+
 	// Update filtered metrics
 	metrics.UpdateFilter(newCfg.Telemetry.AllowedPrefixes,
 		newCfg.Telemetry.BlockedPrefixes)
diff --git a/agent/cache/cache.go b/agent/cache/cache.go
index 44aeb3a046..ed32527e4d 100644
--- a/agent/cache/cache.go
+++ b/agent/cache/cache.go
@@ -144,16 +144,21 @@ type Options struct {
 	EntryFetchRate rate.Limit
 }
 
-// New creates a new cache with the given RPC client and reasonable defaults.
-// Further settings can be tweaked on the returned value.
-func New(options Options) *Cache {
+// applyDefaultValuesOnOptions set default values on options and returned updated value
+func applyDefaultValuesOnOptions(options Options) Options {
 	if options.EntryFetchRate == 0.0 {
 		options.EntryFetchRate = DefaultEntryFetchRate
 	}
 	if options.EntryFetchMaxBurst == 0 {
 		options.EntryFetchMaxBurst = DefaultEntryFetchMaxBurst
 	}
+	return options
+}
 
+// New creates a new cache with the given RPC client and reasonable defaults.
+// Further settings can be tweaked on the returned value.
+func New(options Options) *Cache {
+	options = applyDefaultValuesOnOptions(options)
 	// Initialize the heap. The buffer of 1 is really important because
 	// its possible for the expiry loop to trigger the heap to update
 	// itself and it'd block forever otherwise.
@@ -234,6 +239,28 @@ func (c *Cache) RegisterType(n string, typ Type) {
 	c.types[n] = typeEntry{Name: n, Type: typ, Opts: &opts}
 }
 
+// ReloadOptions updates the cache with the new options
+// return true if Cache is updated, false if already up to date
+func (c *Cache) ReloadOptions(options Options) bool {
+	options = applyDefaultValuesOnOptions(options)
+	if c.options.EntryFetchRate != options.EntryFetchRate || c.options.EntryFetchMaxBurst != options.EntryFetchMaxBurst {
+		c.entriesLock.RLock()
+		defer c.entriesLock.RUnlock()
+		for _, entry := range c.entries {
+			if c.options.EntryFetchRate != options.EntryFetchRate {
+				entry.FetchRateLimiter.SetLimit(options.EntryFetchRate)
+			}
+			if c.options.EntryFetchMaxBurst != options.EntryFetchMaxBurst {
+				entry.FetchRateLimiter.SetBurst(options.EntryFetchMaxBurst)
+			}
+		}
+		c.options.EntryFetchRate = options.EntryFetchRate
+		c.options.EntryFetchMaxBurst = options.EntryFetchMaxBurst
+		return true
+	}
+	return false
+}
+
 // Get loads the data for the given type and request. If data satisfying the
 // minimum index is present in the cache, it is returned immediately. Otherwise,
 // this will block until the data is available or the request timeout is