kevinanew/python-aio-etcd

A python client for etcd

python-aio-etcd documentation

A python client for Etcd https://github.com/coreos/etcd

Official documentation: http://python-aio-etcd.readthedocs.org/

Installation

Pre-requirements

This version of python-etcd will only work correctly with the etcd server version 2.0.x or later. If you are running an older version of etcd, please use python-etcd 0.3.3 or earlier.

This client is known to work with python 3.5. It will not work in older versions of python due to ist use of "async def" syntax.

Python 2 is not supported.

From source

$ python setup.py install

Usage

The basic methods of the client have changed compared to previous versions, to reflect the new API structure; however a compatibility layer has been maintained so that you don't necessarily need to rewrite all your existing code.

Create a client object

import aio_etcd as etcd

client = etcd.Client() # this will create a client against etcd server running on localhost on port 4001
client = etcd.Client(port=4002)
client = etcd.Client(host='127.0.0.1', port=4003)
client = etcd.Client(host=(('127.0.0.1', 4001), ('127.0.0.1', 4002), ('127.0.0.1', 4003)))
client = etcd.Client(host='127.0.0.1', port=4003, allow_redirect=False) # wont let you run sensitive commands on non-leader machines, default is true
# If you have defined a SRV record for _etcd._tcp.example.com pointing to the clients
client = etcd.Client(srv_domain='example.com', protocol="https")

# create a client against https://api.example.com:443/etcd
client = etcd.Client(host='api.example.com', protocol='https', port=443, version_prefix='/etcd')

Write a key

await client.write('/nodes/n1', 1)
# with ttl

await client.set('/nodes/n1', 1)
# Equivalent, for compatibility reasons.

await client.write('/nodes/n2', 2, ttl=4)
# sets the ttl to 4 seconds

Read a key

(await client.read('/nodes/n2')).value
# read a value

(await client.get('/nodes/n2')).value
# Equivalent, for compatibility reasons.

await client.read('/nodes', recursive = True)
# get all the values of a directory, recursively.

# raises etcd.EtcdKeyNotFound when key not found
try:
    client.read('/invalid/path')
except etcd.EtcdKeyNotFound:
    # do something
    print "error"

Delete a key

await client.delete('/nodes/n1')

Atomic Compare and Swap

await client.write('/nodes/n2', 2, prevValue = 4)
# will set /nodes/n2 's value to 2 only if its previous value was 4

await client.write('/nodes/n2', 2, prevExist = False)
# will set /nodes/n2 's value to 2 only if the key did not exist before

await client.write('/nodes/n2', 2, prevIndex = 30)
# will set /nodes/n2 's value to 2 only if the key was last modified at index 30

await client.test_and_set('/nodes/n2', 2, 4)
#equivalent to client.write('/nodes/n2', 2, prevValue = 4)

You can also atomically update a result:

await client.write('/foo','bar')
result = await client.read('/foo')
print(result.value) # bar
result.value += u'bar'
updated = await client.update(result)
# if any other client wrote to '/foo' in the meantime this will fail

print(updated.value) # barbar

Watch a key

result = await client.read('/nodes/n1')
# start from a known initial value

result = await client.read('/nodes/n1', wait = True, waitIndex = result.modifiedIndex+1)
# will wait till the key is changed, and return once it's changed

result = await client.read('/nodes/n1', wait = True, waitIndex = 10)
# get all changes on this key starting from index 10

result = await client.watch('/nodes/n1')
# equivalent to client.read('/nodes/n1', wait = True)

result = await client.watch('/nodes/n1', index = result.modifiedIndex+1)

If you want to time out the read() call, wrap it in asyncio.wait_for:

result = await asyncio.wait_for(client.read('/nodes/n1', wait=True), timeout=30)

Refreshing key TTL

(Since etcd 2.3.0) Keys in etcd can be refreshed without notifying current watchers.

This can be achieved by setting the refresh to true when updating a TTL.

You cannot update the value of a key when refreshing it.

client.write('/nodes/n1', 'value', ttl=30)  # sets the ttl to 30 seconds
client.refresh('/nodes/n1', ttl=600)  # refresh ttl to 600 seconds, without notifying current watchers

Locking module

# Initialize the lock object:
# NOTE: this does not acquire a lock
from aio_etcd.lock import Lock
client = etcd.Client()
# Or you can custom lock prefix, default is '/_locks/' if you are using HEAD
client = etcd.Client(lock_prefix='/my_etcd_root/_locks')
lock = etcd.Lock(client, 'my_lock_name')

# Use the lock object:
await lock.acquire(blocking=True, # will block until the lock is acquired
      lock_ttl=None) # lock will live until we release it
lock.is_acquired  # True
await lock.acquire(lock_ttl=60) # renew a lock
await lock.release() # release an existing lock
lock.is_acquired  # False

# The lock object may also be used as a context manager:
async with Lock(client, 'customer1') as my_lock:
    do_stuff()
    my_lock.is_acquired  # True
    await my_lock.acquire(lock_ttl=60)
my_lock.is_acquired  # False

Get machines in the cluster

machines = await client.machines()

Get leader of the cluster

leaderinfo = await client.leader()

Generate a sequential key in a directory

x = await client.write("/dir/name", "value", append=True)
print("generated key: " + x.key)
# actually the whole path
print("stored value: " + x.value)

List contents of a directory

#stick a couple values in the directory
await client.write("/dir/name", "value1", append=True)
await client.write("/dir/name", "value2", append=True)

directory = await client.get("/dir/name")

# loop through a directory's children
for result in directory.children:
    print(result.key + ": " + result.value)

# or just get the first child value
print(directory.next(children).value)

Development setup

The usual setuptools commands are available.

$ python3 setup.py install

To test, you should have etcd available in your system path:

$ python3 setup.py test

to generate documentation,

$ cd docs
$ make

Release HOWTO

To make a release

1. Update release date/version in NEWS.txt and setup.py
2. Run 'python setup.py sdist'
3. Test the generated source distribution in dist/
4. Upload to PyPI: 'python setup.py sdist register upload'