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@ -1,13 +1,25 @@
etcd
====
## Overview
# etcd
## Start with examples
## Getting Started
### Setting up a node
### Building
etcd is installed like any other Go binary. The steps below will put everything into a directory called etcd.
```
mkdir etcd
cd etcd
export GOPATH=`pwd`
go get github.com/coreos/etcd
go install github.com/coreos/etcd
```
### Running a single node
These examples will use a single node cluster to show you the basics of the etcd REST API. Lets start etcd:
```sh
./etcd
./bin/etcd
```
This will bring up a node, which will be listening on internal port 7001 (for server communication) and external port 4001 (for client communication)
@ -25,31 +37,32 @@ curl http://127.0.0.1:4001/v1/keys/message -d value="Hello world"
```
This response contains five fields. We will introduce three more fields as we try more commands.
1. The action of the request; we set the value via a POST request, thus the action is `SET`.
2. The key of the request; we set `/message` to `Hello world!`, so the key field is `/message`.
2. The key of the request; we set `/message` to `Hello world!`, so the key field is `/message`.
Notice we use a file system like structure to represent the key-value pairs. So each key starts with `/`.
3. The current value of the key; we set the value to`Hello world`.
4. If we set a new key; `/message` did not exist before, so this is a new key.
5. Index field is the unique request index of the set request. Each sensitive request we send to the server will have a unique request index. The current sensitive request are `SET`, `DELETE` and `TESTANDSET`. All of these request will change the state of the key-value store system, thus they are sensitive. `GET`, `LIST` and `WATCH` are non-sensitive commands. Those commands will not change the state of the key-value store system.
You may notice that in this example the index is 3, although it is the first request you sent to the server. This is because there are some internal commands that also change the state of the server, we also need to assign them command indexes(Command used to add a server and sync the servers).
5. Index field is the unique request index of the set request. Each sensitive request we send to the server will have a unique request index. The current sensitive request are `SET`, `DELETE` and `TESTANDSET`. All of these request will change the state of the key-value store system, thus they are sensitive. `GET`, `LIST` and `WATCH` are non-sensitive commands. Those commands will not change the state of the key-value store system. You may notice that in this example the index is 3, although it is the first request you sent to the server. This is because there are some internal commands that also change the state of the server, we also need to assign them command indexes(Command used to add a server and sync the servers).
#### Getting the value of a key
Get the value that we just set in `/message` by issuing a GET:
```sh
curl http://127.0.0.1:4001/v1/keys/message
curl http://127.0.0.1:4001/v1/keys/message
```
You should receive the response as
```json
{"action":"GET","key":"/message","value":"Hello world","index":3}
```
#### Changing the value of a key
We change the value of `/message` from `Hello world` to `Hello etcd`
Change the value of `/message` from `Hello world` to `Hello etcd` with another POST to the key:
```sh
curl http://127.0.0.1:4001/v1/keys/message -d value="Hello etcd"
@ -59,56 +72,57 @@ curl http://127.0.0.1:4001/v1/keys/message -d value="Hello etcd"
{"action":"SET","key":"/message","prevValue":"Hello world","value":"Hello etcd","index":4}
```
There is a new field in the response: prevValue. It is the value of the key before the change happened.
Notice that the `prevValue` is set to `Hello world`.
#### Deleting a key
Remove the `/message` key with a DELETE:
```sh
curl http://127.0.0.1:4001/v1/keys/message -X DELETE
```
You should see the response as
```json
{"action":"DELETE","key":"/message","prevValue":"Hello etcd","index":5}
```
#### Using time to live key
Keys in etcd can be set to expire after a specified number of seconds. That is done by setting a TTL (time to live) on the key when you POST:
```sh
curl http://127.0.0.1:4001/v1/keys/foo -d value=bar -d ttl=5
```
You should see the similar response as (not exact same, they should have different expiration time)
```json
{"action":"SET","key":"/foo","value":"bar","newKey":true,"expiration":"2013-07-11T20:31:12.156146039-07:00","ttl":4,"index":6}
```
There are the last two new fields in response.
Note the last two new fields in response:
Expiration field is the time that this key will expire and be deleted.
1. The expiration is the time that this key will expire and be deleted.
Ttl field is the time to live of the key, it can be derived from current time and expiration time.
2. The ttl is the time to live of the key.
Now you can try to get the key by sending
Now you can try to get the key by sending:
```sh
curl http://127.0.0.1:4001/v1/keys/foo
curl http://127.0.0.1:4001/v1/keys/foo
```
You can expect the ttl is counting down and after 5 seconds you should see this,
If the TTL has passed then you will
```html
404 page not found
```
which indicates the key has expired and was deleted.
#### Watching a prefix
Watch command can watch as a prefix path and get notification if any key changes after the prefix.
We can watch a path prefix and get notifications if any key change under that prefix.
In one terminal, we send a watch request:
```sh
curl http://127.0.0.1:4001/v1/watch/foo
```
@ -121,49 +135,49 @@ In another terminal, we set a key `/foo/foo` to `barbar` to see what will happen
curl http://127.0.0.1:4001/v1/keys/foo/foo -d value=barbar
```
The first terminal should get the notification and return with the same response as the set request.
The first terminal should get the notification and return with the same response as the set request.
```json
{"action":"SET","key":"/foo/foo","value":"barbar","newKey":true,"index":7}
```
OK. Watch command can do more than this. We have index and in etcd we store the most recent 1000 responses by default, which allow us to watch for previous commands.
However, the watch command can do more than this. Using the the index we can watch for commands that has happened in the past. This is useful for ensuring you don't miss events between watch commands.
Let us try to watch for the set command of index 6 again.
Let's try to watch for the set command of index 6 again:
```sh
curl http://127.0.0.1:4001/v1/watch/foo -d index=7
```
You should see the watch command return immediately with the same response as previous.
The watch command returns immediately with the same response as previous.
#### Trying TestAndSet
#### Atomic Test and Set
Etcd servers will process all the command in sequence atomically, thus it can be used as a centralized decision making cluster.
Etcd servers will process all the command in sequence atomically. Thus it can be used as a centralized coordination service in a cluster.
TestAndSet is the most basic operation to build distributed lock service and more interesting stuff.
`TestAndSet` is the most basic operation to build distributed lock service.
What it does is to test whether the given previous value is equal to the value of the key, if equal etcd will change the value of the key to the given value.
The basic logic is to test whether the given previous value is equal to the value of the key, if equal etcd will change the value of the key to the given value.
Here is a simple example. Let's create a key-value pair first: `testAndSet=one`.
Here is a simple example.
Let us create a key-value pair first: `testAndSet=one`.
```sh
curl http://127.0.0.1:4001/v1/keys/testAndSet -d value=one
```
Let us try a invaild `TestAndSet` command.
Let's try an invaild `TestAndSet` command.
```sh
curl http://127.0.0.1:4001/v1/testAndSet/testAndSet -d prevValue=two -d value=three
```
This will try to test if the previous of the key is two, it is change it to three.
The response should be
```html
Test one==two fails
```
which means `testAndSet` failed.
which means `testAndSet` failed.
Let us try a vaild one.
@ -171,16 +185,17 @@ Let us try a vaild one.
curl http://127.0.0.1:4001/v1/testAndSet/testAndSet -d prevValue=one -d value=two
```
The response should be
The response should be
```json
{"action":"SET","key":"/testAndSet","prevValue":"one","value":"two","index":10}
```
We successfully change the value from “one” to “two”, since we give the correct previous value.
We successfully changed the value from “one” to “two”, since we give the correct previous value.
#### Listing directory
Last we provide a simple List command to list all the keys under a prefix path.
Let us create some keys first.
@ -199,7 +214,7 @@ Let us list them next.
curl http://127.0.0.1:4001/v1/list/foo/
```
We should see the response as
We should see the response as
```json
{"Key":"foo","Value":"barbar","Type":"f"} {"Key":"foo_dir","Value":".","Type":"d"}
@ -208,11 +223,10 @@ We should see the response as
which meas `foo=barbar` is a key-value pair under `/foo` and `foo_dir` is a directory.
### Setting up a cluster of three machines
Next we can explore the power of etcd cluster. We use go-raft as the underlay distributed protocol which provide consistency and persistence of all the machines in the cluster. The will allow if the minor machine dies, the cluster will still be able to performance correctly. Also if most of the machines dead and restart, we will recover from the previous state of the cluster.
Let us create 3 new machines.
Next let's explore the use of etcd clustering. We use go-raft as the underlying distributed protocol which provides consistency and persistence of the data across all of the etcd instances.
The first one will be
Let start by creating 3 new etcd instances.
We use -s to specify server port and -c to specify client port and -d to specify the directory to store the log and info of the node in the cluster
@ -220,19 +234,14 @@ We use -s to specify server port and -c to specify client port and -d to specify
./etcd -s 7001 -c 4001 -d nodes/node1
```
We use -C to specify the Cluster
Let the join two more nodes to this cluster using the -C argument:
Let the second one join it.
```sh
./etcd -c 4002 -s 7002 -C 127.0.0.1:7001 -d nod/node2
```
And the third one:
```sh
./etcd -c 4003 -s 7003 -C 127.0.0.1:7001 -d nod/node3
```
Let us add a key to the cluster of 3 nodes.
Now we can do normal SET and GET operations on keys as we explored earlier.
```sh
curl http://127.0.0.1:4001/v1/keys/foo -d value=bar
@ -242,17 +251,15 @@ curl http://127.0.0.1:4001/v1/keys/foo -d value=bar
{"action":"SET","key":"/foo","value":"bar","newKey":true,"index":5}
```
Let us kill the leader of the cluster to see what will happen.
#### Killing Nodes in the Cluster
Kill the first node which is the current leader
Try to get the value from the other machine
Let's kill the leader of the cluster and get the value from the other machine:
```sh
curl http://127.0.0.1:4002/v1/keys/foo
```
You should be able to see this
You should be able to see this:
```json
{"action":"GET","key":"/foo","value":"bar","index":5}
@ -260,13 +267,16 @@ You should be able to see this
It succeed!
OK. Next let us kill all the nodes to test persistence. And restart all the nodes use the same command before.
#### Testing Persistence
OK. Next let us kill all the nodes to test persistence. And restart all the nodes use the same command as before.
Your request for the `foo` key will return the correct value:
Try
```sh
curl http://127.0.0.1:4002/v1/keys/foo
```
You should able to see
```json
{"action":"GET","key":"/foo","value":"bar","index":5}
```