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from datetime import timedelta |
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from socket import gethostname |
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import sys |
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from uuid import uuid4 |
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from kazoo.client import KazooClient |
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from st2actions.runners.pythonrunner import Action |
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class NonBlockingLease(Action): |
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""" |
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Exclusive lease that does not block. |
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An exclusive lease ensures that only one client at a time owns the lease. |
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The action exits successfully if the lease was obtained and with code 1 otherwise. |
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A common use case is a situation where a task should only run on a single host. In this case, |
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the clients that did not obtain the lease should exit without performing the protected task. |
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The lease stores time stamps using client clocks, and will therefore only work if client clocks |
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are roughly synchronised. It uses UTC, and works across time zones and daylight savings. |
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""" |
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# NOTE: the drift on the clocks running cronjobs controlled by this lease must be |
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# less than the frequency - the lease_time. For example, a cronjob running every |
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# minute with a lease_time of 30s means that your clocks must all be within 30s of |
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# each other or nobody will ever get the lease. |
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# |
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# Changing the threshold allows you to decide whether it's more important that |
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# the job always runs (and sometimes twice) or if it's better to run only once |
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# or not at all. With a lease_time of 50, if clocks drift by more than 10s, it |
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# will appear as though the lease is always taken and your job will never run. |
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# (Conversely, with a lease_time of 10 and a drift of >10s, two hosts will both |
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# get a lease, running your job twice.) |
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def __init__(self, config): |
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super(NonBlockingLease, self).__init__(config) |
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self.hosts = self.config['zookeeper_hosts'] |
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self.root = self.config['zookeeper_root'] |
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def run(self, lease_name, lease_time): |
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zk = KazooClient(hosts=self.hosts) |
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zk.start() |
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path = "%s/%s" % (self.root, lease_name) |
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# unique id ensures only one action execution if multiple executions on the same host |
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identifier = '%s: %s' % (gethostname(), uuid4()) |
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duration = timedelta(seconds=lease_time) |
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lease = zk.NonBlockingLease(path, duration, identifier=identifier) |
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if not lease: |
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sys.exit(1) |
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StackStorm /
st2contrib
