consullock 1.1.0

Tool to use locks in Consul (v1.1.0)

Consul Lock

CLI and Python interface for easily managing Consul locks

About

• CLI & Python interface:

  • Acquire and release a lock.

  • Set TTL of the session that acquires a lock.

  • Blocking and non-blocking locking.

  • Lock acquire timeouts.

  • Add extra metadata to lock information (useful for monitoring who is holding locks).

• CLI:

  • Release multiple locks with keys that match regular expression.

  • Meaningful exit codes (see configuration.py for details).

  • JSON output on stdout.

  • Add extra verbosity on stderr with -vv.

• Python interface:

  • Release multiple locks.

  • Find and release multiple locks with keys that match regular expression.

  • Type hinting.

Installation

Prerequisites: - python >= 3.6

The tool can be installed from PyPi:

pip install consullock

Bleeding edge versions can be installed directly from GitHub:

pip install git+https://github.com/wtsi-hgi/consul-lock.git@master#egg=consullock

Usage

CLI

Setup

Set environment variables:

export CONSUL_HTTP_ADDR=consul.example.com:8500
export CONSUL_HTTP_TOKEN=token

General

usage: consul-lock [-h] [-v] {unlock,lock} ...

Tool to use locks in Consul

positional arguments:
  {unlock,lock}  action
    unlock       release a lock
    lock         acquire a lock

optional arguments:
  -h, --help     show this help message and exit
  -v             increase the level of log verbosity (add multiple increase
                 further)

Locking

usage: consul-lock lock [-h] [--session-ttl SESSION_TTL] [--non-blocking]
                        [--timeout TIMEOUT]
                        key

positional arguments:
  key                   the lock identifier

optional arguments:
  -h, --help            show this help message and exit
  --session-ttl SESSION_TTL
                        time to live (ttl) in seconds of the session that will
                        be created to hold the lock. Must be between 10s and
                        86400s (inclusive). If set to 0, the session will not
                        expire
  --non-blocking        do not block if cannot lock straight away
  --timeout TIMEOUT     give up trying to acquire the key after this many
                        seconds (where 0 is never)
  --metadata METADATA   additional metadata to add to the lock information
                        (will be converted to JSON)

Unlocking

usage: consul-lock unlock [-h] [-r] key

positional arguments:
  key         the lock identifier

optional arguments:
  -h, --help  show this help message and exit
  -r          Whether the key should be treated as a regular expression and to
              release all matching locks

Examples

Block until acquires lock with key “my/lock”, which will expire after 10 minutes:

$ consul-lock lock --session-ttl=600 my/lock
{"created": "2017-11-30T14:55:49.322108", "key": "my/lock", "secondsToLock": 2.6241003070026636e-05, "session": "9b92744f-f1a9-db12-7873-ad44af5ae224"}
$ echo $?
0

Try to acquire already locked “my/lock” but do not block:

$ consul-lock lock --non-blocking my/lock
null
Unable to acquire lock: my/lock
$ echo $?
100

(where null is the JSON output, written to stdout)

Add metadata to lock:

$ consul-lock lock --metadata={"testing": 123} my/lock
{"created": "2017-12-05T12:26:13.717995", "key": "my/lock", "metadata": {"testing": 123}, "secondsToLock": 4.327880731027108, "session": "6ad662de-6e0c-8e0f-d92c-5fface60c49b"}

Unlock lock:

$ consul-lock unlock my/lock
["my/lock"]
$ echo $?
0

Python

from typing import Set
from consullock.configuration import get_consul_configuration_from_environment
from consullock.managers import ConsulLockManager
from consullock.models import ConsulLockInformation

# Instantiate lock manager
lock_manager = ConsulLockManager(
    consul_configuration=get_consul_configuration_from_environment(),
    session_ttl_in_seconds=3600)

# Get lock
lock = lock_manager.acquire("my/lock", timeout=60, blocking=True, metadata="testing")   # type: ConsulLockInformation

# Find locks
locks = lock_manager.find("my/.*")  # type: Dict[str, Optional[ConsulLockInformation]]

# Release single lock
lock_manager.release("my/lock")

# Release many locks
lock_manager.release_all("my/lock-1", "my/lock-2", "my/lock-3")

# Release locks with key matching regex
lock_manager.release_regex("my/.*")

Development

Tests

Prerequisites: - Docker (used to start Consul instances)

Install the test requirements:

pip install -r test_requirements.txt

Run tests with:

PYTHONPATH=. python -m unittest discover -v -s consullock/tests

Alternatives

• alaa/consul-lock - Go tool with CLI where the user has to deal with sessions.

• fidian/consul-locker - bash script that locks, executes and then releases.

• KurToMe/python-consul-lock - unmaintained Python lock interface with with questionable configuration.