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import json
from collections import defaultdict
import datetime
# freq to write cached state to disk
PERSIST_PERIOD = datetime.timedelta(seconds = 10)
# on disk key prefix
HEALTH_HISTORY_KEY_PREFIX = "health_history/"
# apply on offset to "now": used for testing
NOW_OFFSET = None
class HealthEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj, set):
return list(obj)
return json.JSONEncoder.default(self, obj)
class HealthCheckAccumulator(object):
"""
Deuplicated storage of health checks.
"""
def __init__(self, init_checks = None):
# check : severity : { summary, detail }
# summary and detail are deduplicated
self._checks = defaultdict(lambda:
defaultdict(lambda: {
"summary": set(),
"detail": set()
}))
if init_checks:
self._update(init_checks)
def __str__(self):
return "check count {}".format(len(self._checks))
def add(self, checks):
"""
Add health checks to the current state
Returns:
bool: True if the state changed, False otherwise.
"""
changed = False
for check, info in checks.items():
# only keep the icky stuff
severity = info["severity"]
if severity == "HEALTH_OK":
continue
summary = info["summary"]["message"]
details = map(lambda d: d["message"], info["detail"])
if self._add_check(check, severity, [summary], details):
changed = True
return changed
def checks(self):
return self._checks
def merge(self, other):
assert isinstance(other, HealthCheckAccumulator)
self._update(other._checks)
def _update(self, checks):
"""Merge checks with same structure. Does not set dirty bit"""
for check in checks:
for severity in checks[check]:
summaries = set(checks[check][severity]["summary"])
details = set(checks[check][severity]["detail"])
self._add_check(check, severity, summaries, details)
def _add_check(self, check, severity, summaries, details):
changed = False
for summary in summaries:
if summary not in self._checks[check][severity]["summary"]:
changed = True
self._checks[check][severity]["summary"].add(summary)
for detail in details:
if detail not in self._checks[check][severity]["detail"]:
changed = True
self._checks[check][severity]["detail"].add(detail)
return changed
class HealthHistorySlot(object):
"""
Manage the life cycle of a health history time slot.
A time slot is a fixed slice of wall clock time (e.g. every hours, from :00
to :59), and all health updates that occur during this time are deduplicated
together. A slot is initially in a clean state, and becomes dirty when a new
health check is observed. The state of a slot should be persisted when
need_flush returns true. Once the state has been flushed, reset the dirty
bit by calling mark_flushed.
"""
def __init__(self, init_health = dict()):
self._checks = HealthCheckAccumulator(init_health.get("checks"))
self._slot = self._curr_slot()
self._next_flush = None
def __str__(self):
return "key {} next flush {} checks {}".format(
self.key(), self._next_flush, self._checks)
def health(self):
return dict(checks = self._checks.checks())
def key(self):
"""Identifier in the persist store"""
return self._key(self._slot)
def expired(self):
"""True if this slot is the current slot, False otherwise"""
return self._slot != self._curr_slot()
def need_flush(self):
"""True if this slot needs to be flushed, False otherwise"""
now = HealthHistorySlot._now()
if self._next_flush is not None:
if self._next_flush <= now or self.expired():
return True
return False
def mark_flushed(self):
"""Reset the dirty bit. Caller persists state"""
assert self._next_flush
self._next_flush = None
def add(self, health):
"""
Add health to the underlying health accumulator. When the slot
transitions from clean to dirty a target flush time is computed.
"""
changed = self._checks.add(health["checks"])
if changed and not self._next_flush:
self._next_flush = HealthHistorySlot._now() + PERSIST_PERIOD
return changed
def merge(self, other):
assert isinstance(other, HealthHistorySlot)
self._checks.merge(other._checks)
@staticmethod
def key_range(hours):
"""Return the time slot keys for the past N hours"""
def inner(curr, hours):
slot = curr - datetime.timedelta(hours = hours)
return HealthHistorySlot._key(slot)
curr = HealthHistorySlot._curr_slot()
return map(lambda i: inner(curr, i), range(hours))
@staticmethod
def curr_key():
"""Key for the current UTC time slot"""
return HealthHistorySlot._key(HealthHistorySlot._curr_slot())
@staticmethod
def key_to_time(key):
"""Return key converted into datetime"""
timestr = key[len(HEALTH_HISTORY_KEY_PREFIX):]
return datetime.datetime.strptime(timestr, "%Y-%m-%d_%H")
@staticmethod
def _key(dt):
"""Key format. Example: health_2018_11_05_00"""
return HEALTH_HISTORY_KEY_PREFIX + dt.strftime("%Y-%m-%d_%H")
@staticmethod
def _now():
"""Control now time for easier testing"""
now = datetime.datetime.utcnow()
if NOW_OFFSET is not None:
now = now + NOW_OFFSET
return now
@staticmethod
def _curr_slot():
"""Slot for the current UTC time"""
dt = HealthHistorySlot._now()
return datetime.datetime(
year = dt.year,
month = dt.month,
day = dt.day,
hour = dt.hour)
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