I was working with kubernetes and there is a tool named etcd used in kubernetes architecture, so I checked wikipedia for it:

etcd is a persistent, lightweight, distributed, key-value data store developed by CoreOS …

And I was like, so this etcd thingy can be used to store keys and some values?

interesting

So I gave it a try, the binaries for etcd are here and you can run etcd simply by ./etcd command.

etcdctl

In compressed file there is a executable named etcdctl which can be used to work with a running etcd service:

# set values
$ ./etcdctl set key value
value
$ ./etcdctl set key1 value1
value1

# get values
$ ./etcdctl get key
value

# set values but expire them after 5 seconds
./etcdctl set expire_me value --ttl 5
value

# list existing keys
$ ./etcdctl ls
/key
/key1

A you have seen in above samples etcd uses a file-system-like structure to represent keys, therefore you can create directories in etcd:

$ ./etcdctl set /the/parent/directories/key value
value

$ ./etcdctl get /the # or the
/the: is a directory

$ ./etcdctl set /the value # or the
Error:  102: Not a file (/the)

$ ./etcdctl set /the/topkey topvalue
topvalue

$ ./etcdctl ls /the -r
/the/parent
/the/parent/directories
/the/parent/directories/key
/the/topkey

API

etcdctl is cool and all but I need something to set values in etcd from my code, some kind of API to work with etcd, something like this. here are the curl samples from API guide:

# set key
curl http://127.0.0.1:2379/v2/keys/message -XPUT -d value="Hello world"
# get key
curl http://127.0.0.1:2379/v2/keys/message

So here is the python snippet to set a key:

# set.py
import requests

resp = requests.put(
    "http://127.0.0.1:2379/v2/keys/message",
    data={"value": "this is the value"},
)

print(resp.status_code)
print(resp.json())

# 201
# {
#   'action': 'set',
#   'node': {
#       'key': '/message',
#       'value': 'this is the value',
#       'modifiedIndex': 15,
#       'createdIndex': 15
#   }
# }

And here is the snippet to get that key:

# get.py
import requests

resp = requests.get("http://127.0.0.1:2379/v2/keys/message")

print(resp.status_code)
print(resp.json())

# 200
# {
#   'action': 'get',
#   'node': {
#       'key': '/message',
#       'value': 'this is the value',
#       'modifiedIndex': 15,
#       'createdIndex': 15
#   }
# }

Let’s use etcdctl just to be sure:

$ ./etcdctl get /message
this is the value

So what?

That’s it. If you are confused by seeing many different names in kubernetes architecture this small post was trying you help you see etcd as a simple key/value store. I hope this post cleared something up for you.