Update the docs with a section regarding the cache usage

Signed-off-by: Soule BA <soule@weave.works>

controllers/helmchart_controller.go

@@ -463,10 +463,8 @@ func (r *HelmChartReconciler) buildFromHelmRepository(ctx context.Context, obj *
 
  // Try to retrieve the repository index from the cache
  if r.Cache != nil {
- if index, found := r.Cache.Get(r.Storage.LocalPath(*repo.GetArtifact())); err == nil {
- if found {
- chartRepo.Index = index.(*helmrepo.IndexFile)
- }
+ if index, found := r.Cache.Get(r.Storage.LocalPath(*repo.GetArtifact())); found {
+ chartRepo.Index = index.(*helmrepo.IndexFile)
  }
  }
 
@@ -502,7 +500,7 @@ func (r *HelmChartReconciler) buildFromHelmRepository(ctx context.Context, obj *
  // Using r.Storage.LocalPath(*repo.GetArtifact() is safe as the path is in the format /<helm-repository-name>/<chart-name>/<filename>.
  err := r.Cache.Set(r.Storage.LocalPath(*repo.GetArtifact()), chartRepo.Index, r.TTL)
  if err != nil {
- r.eventLogf(ctx, obj, events.EventTypeTrace, sourcev1.CacheOperationFailedReason, "failed to cache index: %v", err)
+ r.eventLogf(ctx, obj, events.EventTypeTrace, sourcev1.CacheOperationFailedReason, "failed to cache index: %s", err)
  }
 
  }

docs/spec/v1beta2/helmcharts.md

@@ -390,6 +390,53 @@ Besides being reported in Events, the reconciliation errors are also logged by
 the controller. The Flux CLI offer commands for filtering the logs for a
 specific HelmChart, e.g. `flux logs --level=error --kind=HelmChart --name=<chart-name>`.
 
+### Improving resource consumption by enabling the cache
+
+When using a `HelmRepository` as Source for a `HelmChart`, the controller loads
+the repository index in memory to find the latest version of the chart.
+
+The controller can be configured to cache Helm repository indexes in memory.
+The cache is used to avoid loading repository indexes for every `HelmChart`
+reconciliation.
+
+The following flags are provided to enable and configure the cache:
+- `helm-cache-max-size`: The maximum size of the cache in number of indexes.
+ If `0`, then the cache is disabled.
+- `helm-cache-ttl`: The TTL of an index in the cache.
+- `helm-cache-purge-interval`: The interval at which the cache is purged of
+ expired items. 
+
+The caching strategy is to pull a repository index from the cache if it is 
+available, otherwise to load the index, retrieve and build the chart,
+then cache the index. The cached index TTL is refreshed every time the
+Helm repository index is loaded with the `helm-cache-ttl` value.
+
+The cache is purged of expired items every `helm-cache-purge-interval`.
+
+When the cache is full, no more items can be added to the cache, and the
+source-controller will report a warning event instead.
+
+In order to use the cache, set the related flags in the source-controller
+Deployment config:
+
+```yaml
+ spec:
+ containers:
+ - args:
+ - --watch-all-namespaces
+ - --log-level=info
+ - --log-encoding=json
+ - --enable-leader-election
+ - --storage-path=/data
+ - --storage-adv-addr=source-controller.$(RUNTIME_NAMESPACE).svc.cluster.local.
+ ## Helm cache with up to 10 items, i.e. 10 indexes.
+ - --helm-cache-max-size=10
+ ## TTL of an index is 1 hour.
+ - --helm-cache-ttl=1h
+ ## Purge expired index every 10 minutes.
+ - --helm-cache-purge-interval=10m
+```
+
 ## HelmChart Status
 
 ### Artifact

internal/cache/cache.go

@@ -26,14 +26,16 @@ type Cache struct {
 
 // Item is an item stored in the cache.
 type Item struct {
- Object interface{}
+ // Object is the item's value.
+ Object interface{}
+ // Expiration is the item's expiration time.
  Expiration int64
 }
 
 type cache struct {
  // Items holds the elements in the cache.
  Items map[string]Item
- // Maximum number of items the cache can hold.
+ // MaxItems is the maximum number of items the cache can hold.
  MaxItems int
  mu sync.RWMutex
  janitor *janitor
@@ -82,6 +84,9 @@ func (c *cache) Set(key string, value interface{}, expiration time.Duration) err
  return fmt.Errorf("Cache is full")
 }
 
+// Add an item to the cache, existing items will not be overwritten.
+// To overwrite existing items, use Set.
+// If the cache is full, Add will return an error.
 func (c *cache) Add(key string, value interface{}, expiration time.Duration) error {
  c.mu.Lock()
  _, found := c.Items[key]
@@ -100,6 +105,8 @@ func (c *cache) Add(key string, value interface{}, expiration time.Duration) err
  return fmt.Errorf("Cache is full")
 }
 
+// Get an item from the cache. Returns the item or nil, and a bool indicating
+// whether the key was found.
 func (c *cache) Get(key string) (interface{}, bool) {
  c.mu.RLock()
  item, found := c.Items[key]
@@ -117,18 +124,23 @@ func (c *cache) Get(key string) (interface{}, bool) {
  return item.Object, true
 }
 
+// Delete an item from the cache. Does nothing if the key is not in the cache.
 func (c *cache) Delete(key string) {
  c.mu.Lock()
  delete(c.Items, key)
  c.mu.Unlock()
 }
 
+// Clear all items from the cache.
+// This reallocate the inderlying array holding the items,
+// so that the memory used by the items is reclaimed.
 func (c *cache) Clear() {
  c.mu.Lock()
  c.Items = make(map[string]Item)
  c.mu.Unlock()
 }
 
+// HasExpired returns true if the item has expired.
 func (c *cache) HasExpired(key string) bool {
  c.mu.RLock()
  item, ok := c.Items[key]
@@ -146,6 +158,8 @@ func (c *cache) HasExpired(key string) bool {
  return false
 }
 
+// SetExpiration sets the expiration for the given key.
+// Does nothing if the key is not in the cache.
 func (c *cache) SetExpiration(key string, expiration time.Duration) {
  c.mu.Lock()
  item, ok := c.Items[key]
@@ -157,6 +171,9 @@ func (c *cache) SetExpiration(key string, expiration time.Duration) {
  c.mu.Unlock()
 }
 
+// GetExpiration returns the expiration for the given key.
+// Returns zero if the key is not in the cache or the item
+// has already expired.
 func (c *cache) GetExpiration(key string) time.Duration {
  c.mu.RLock()
  item, ok := c.Items[key]
@@ -174,6 +191,7 @@ func (c *cache) GetExpiration(key string) time.Duration {
  return time.Duration(item.Expiration - time.Now().UnixNano())
 }
 
+// DeleteExpired deletes all expired items from the cache.
 func (c *cache) DeleteExpired() {
  c.mu.Lock()
  for k, v := range c.Items {
@@ -185,12 +203,12 @@ func (c *cache) DeleteExpired() {
 }
 
 type janitor struct {
- Interval time.Duration
+ interval time.Duration
  stop chan bool
 }
 
-func (j *janitor) Run(c *cache) {
- ticker := time.NewTicker(j.Interval)
+func (j *janitor) run(c *cache) {
+ ticker := time.NewTicker(j.interval)
  for {
  select {
  case <-ticker.C:
@@ -206,20 +224,21 @@ func stopJanitor(c *Cache) {
  c.janitor.stop <- true
 }
 
+// New creates a new cache with the given configuration.
 func New(maxItems int, interval time.Duration) *Cache {
  c := &cache{
  Items: make(map[string]Item),
  MaxItems: maxItems,
  janitor: &janitor{
- Interval: interval,
+ interval: interval,
  stop: make(chan bool),
  },
  }
 
  C := &Cache{c}
 
  if interval > 0 {
- go c.janitor.Run(c)
+ go c.janitor.run(c)
  runtime.SetFinalizer(C, stopJanitor)
  }
 

main.go

@@ -115,9 +115,9 @@ func main() {
  flag.DurationVar(&requeueDependency, "requeue-dependency", 30*time.Second,
  "The interval at which failing dependencies are reevaluated.")
  flag.IntVar(&helmCacheMaxSize, "helm-cache-max-size", 0,
- "The maximum size of the cache in number of items.")
+ "The maximum size of the cache in number of indexes.")
  flag.StringVar(&helmCacheTTL, "helm-cache-ttl", "15m",
- "The TTL of an item in the cache. Valid time units are ns, us (or µs), ms, s, m, h.")
+ "The TTL of an index in the cache. Valid time units are ns, us (or µs), ms, s, m, h.")
  flag.StringVar(&helmCachePurgeInterval, "helm-cache-purge-interval", "1m",
  "The interval at which the cache is purged. Valid time units are ns, us (or µs), ms, s, m, h.")