#96 implement exponential backoff

kube_ops_view/backoff.py

@@ -0,0 +1,48 @@
+import random
+
+
+def expo(n: int, base=2, factor=1, max_value=None):
+    """Exponential decay.
+
+    Adapted from https://github.com/litl/backoff/blob/master/backoff.py (MIT License)
+
+    Args:
+        base: The mathematical base of the exponentiation operation
+        factor: Factor to multiply the exponentation by.
+        max_value: The maximum value to yield. Once the value in the
+             true exponential sequence exceeds this, the value
+             of max_value will forever after be yielded.
+    """
+    a = factor * base ** n
+    if max_value is None or a < max_value:
+        return a
+    else:
+        return max_value
+
+
+def random_jitter(value, jitter=1):
+    """Jitter the value a random number of milliseconds.
+
+    Copied from https://github.com/litl/backoff/blob/master/backoff.py (MIT License)
+
+    This adds up to 1 second of additional time to the original value.
+    Prior to backoff version 1.2 this was the default jitter behavior.
+    Args:
+        value: The unadulterated backoff value.
+    """
+    return value + random.uniform(0, jitter)
+
+
+def full_jitter(value):
+    """Jitter the value across the full range (0 to value).
+
+    Copied from https://github.com/litl/backoff/blob/master/backoff.py (MIT License)
+
+    This corresponds to the "Full Jitter" algorithm specified in the
+    AWS blog's post on the performance of various jitter algorithms.
+    (http://www.awsarchitectureblog.com/2015/03/backoff.html)
+
+    Args:
+        value: The unadulterated backoff value.
+    """
+    return random.uniform(0, value)

kube_ops_view/main.py

@@ -89,6 +89,7 @@ def event(cluster_ids: set):
     for cluster_id in (app.store.get('cluster-ids') or []):
         if not cluster_ids or cluster_id in cluster_ids:
             cluster = app.store.get(cluster_id)
+            if cluster:
                 yield 'event: clusterupdate\ndata: ' + json.dumps(cluster, separators=(',', ':')) + '\n\n'
     while True:
         for event_type, event_data in app.store.listen():

kube_ops_view/update.py

@@ -0,0 +1,82 @@
+import logging
+import time
+
+import gevent
+import json_delta
+import requests.exceptions
+
+from .backoff import expo, random_jitter
+
+logger = logging.getLogger(__name__)
+
+
+def calculate_backoff(tries: int):
+    return random_jitter(expo(tries, factor=2, max_value=120), jitter=4)
+
+
+def get_short_error_message(e: requests.exceptions.RequestException):
+    '''Generate a reasonable short message why the HTTP request failed'''
+
+    if e.response is not None:
+        # e.g. "401 Unauthorized"
+        return '{} {}'.format(e.response.status_code, e.response.reason)
+    elif isinstance(e, requests.exceptions.ConnectionError):
+        # e.g. "ConnectionError" or "ConnectTimeout"
+        return e.__class__.__name__
+    else:
+        return str(e)
+
+
+def update_clusters(cluster_discoverer, query_cluster: callable, store, debug: bool):
+    while True:
+        lock = store.acquire_lock()
+        if lock:
+            try:
+                clusters = cluster_discoverer.get_clusters()
+                cluster_ids = set()
+                for cluster in clusters:
+                    cluster_ids.add(cluster.id)
+                    backoff_key = '{}:backoff'.format(cluster.id)
+                    backoff = store.get(backoff_key)
+                    if backoff and time.time() < backoff['next_try']:
+                        # cluster is still in backoff, skip
+                        continue
+                    try:
+                        data = query_cluster(cluster)
+                    except Exception as e:
+                        if not backoff:
+                            backoff = {}
+                        tries = backoff.get('tries', 0) + 1
+                        backoff['tries'] = tries
+                        wait_seconds = calculate_backoff(tries)
+                        backoff['next_try'] = time.time() + wait_seconds
+                        if isinstance(e, requests.exceptions.RequestException):
+                            message = get_short_error_message(e)
+                            log = logger.error
+                        else:
+                            message = str(e)
+                            log = logger.exception
+                        log('Failed to query cluster {} ({}): {} (try {}, wait {} seconds)'.format(
+                            cluster.id, cluster.api_server_url, message, tries, round(wait_seconds)))
+                        store.set(backoff_key, backoff)
+                    else:
+                        if backoff:
+                            # reset backoff
+                            store.set(backoff_key, None)
+                        old_data = store.get(data['id'])
+                        if old_data:
+                            # https://pikacode.com/phijaro/json_delta/ticket/11/
+                            # diff is extremely slow without array_align=False
+                            delta = json_delta.diff(old_data, data, verbose=debug, array_align=False)
+                            store.publish('clusterdelta', {'cluster_id': cluster.id, 'delta': delta})
+                            if delta:
+                                store.set(cluster.id, data)
+                        else:
+                            store.publish('clusterupdate', data)
+                            store.set(cluster.id, data)
+                store.set('cluster-ids', list(sorted(cluster_ids)))
+            except:
+                logger.exception('Failed to update')
+            finally:
+                store.release_lock(lock)
+        gevent.sleep(5)