Building datastore

In order to persist the Kubernetes cluster information, we need to set up datastore. Kubernetes uses etcd as a standard datastore. This section will guide you to build the etcd server.

How to do it…

The etcd database requires Linux OS; some Linux distributions provide the etcd package and some don't. This section describes how to install etcd.

Red Hat Enterprise Linux 7 or CentOS 7

Red Hat Enterprise Linux (RHEL) 7, CentOS 7 or later has an official package for etcd. You can install via the yum command, as follows:

//it will perform to install etcd package on RHEL/CentOS Linux
sudo yum update -y
sudo yum install etcd

Ubuntu Linux 15.10 Wily Werewolf

Ubuntu 15.10 or later has an official package for etcd as well. You can install via the apt-get command as follows:

//it will perform to install etcd package on Ubuntu Linux
sudo apt-get update -y
sudo apt-get install etcd

Other Linux

If you are using a different Linux version, such as Amazon Linux, you can download a binary from the official website and install it as follows.

Download a binary

etcd is provided via https://github.com/coreos/etcd/releases. OS X (darwin-amd64), Linux, Windows binary, and source code are available for download.

Tip

Note that there are no 32-bit binaries provided due to the Go runtime issue. You must prepare a 64-bit Linux OS.

Download a binary

On your Linux machine, use the curl command to download the etcd-v2.2.1-linux-amd64.tar.gz binary:

// follow redirection(-L) and use remote name (-O)
curl -L -O https://github.com/coreos/etcd/releases/download/v2.2.1/etcd-v2.2.1-linux-amd64.tar.gz
Download a binary

Creating a user

Due to security reasons, create a local user and group that can own etcd packages:

  1. Run the following useradd command:
    //options
//    create group(-U), home directory(-d), and create it(-m)
//    name in GCOS field (-c), login shell(-s)
$ sudo useradd -U -d /var/lib/etcd -m -c "etcd user" -s /sbin/nologin etcd
  2. You can check /etc/passwd to see whether creating etcd user has created a user or not:
    //search etcd user on /etc/passwd, uid and gid is vary
$ grep etcd /etc/passwd
etcd:x:997:995:etcd user:/var/lib/etcd:/sbin/nologin

    Tip

    You can delete a user any time; type sudo userdel -r etcd to delete etcd user.

Install etcd

  1. After downloading an etcd binary, use the tar command to extract files:
    $ tar xf etcd-v2.2.1-linux-amd64.tar.gz 
$ cd etcd-v2.2.1-linux-amd64

//use ls command to see that there are documentation and binaries 
$ ls
Documentation  README-etcdctl.md  README.md  etcd  etcdctl
  2. There are etcd daemon and etcdctl command that need to be copied to /usr/local/bin. Also, create /etc/etcd/etcd.conf as a setting file:
    $ sudo cp etcd etcdctl /usr/local/bin/

//create etcd.conf
$ sudo mkdir -p /etc/etcd/
$ sudo touch /etc/etcd/etcd.conf
$ sudo chown -R etcd:etcd /etc/etcd

How it works…

Let's test run the etcd daemon to explorer the etcd functionalities. Type the etcd command with the name and data-dir argument as follows:

//for the testing purpose, create data file under /tmp
$ etcd --name happy-etcd --data-dir /tmp/happy.etcd &

Then, you will see several output logs as follows:

How it works…

Now, you can try to use the etcdctl command to access etcd and to load and store the data as follows:

//set value "hello world" to the key /my/happy/data 
$ etcdctl set /my/happy/data "hello world"

//get value for key /my/happy/data
$ etcdctl get /my/happy/data
hello world

In addition, by default, etcd opens TCP port 2379 to access the RESTful API, so you may also try to use an HTTP client, such as the curl command to access data as follows:

//get value for key /my/happy/data using cURL
$ curl -L http://localhost:2379/v2/keys/my/happy/data
{"action":"get","node":{"key":"/my/happy/data","value":"hello world","modifiedIndex":4,"createdIndex":4}}

//set value "My Happy world" to the key /my/happy/data using cURL
$ curl http://127.0.0.1:2379/v2/keys/my/happy/data -XPUT -d value="My Happy world"

//get value for key /my/happy/data using etcdctl 
$ etcdctl get /my/happy/data
My Happy world

Okay! Now, you can delete the key using the curl command as follows:

$ curl http://127.0.0.1:2379/v2/keys/my?recursive=true -XDELETE

//no more data returned afterword
$ curl http://127.0.0.1:2379/v2/keys/my/happy/data
{"errorCode":100,"message":"Key not found","cause":"/my","index":10}

$ curl http://127.0.0.1:2379/v2/keys/my/happy
{"errorCode":100,"message":"Key not found","cause":"/my","index":10}

$ curl http://127.0.0.1:2379/v2/keys/my
{"errorCode":100,"message":"Key not found","cause":"/my","index":10}

Auto startup script

Based on your Linux, either systemd or init, there are different ways to make an auto startup script.

If you are not sure, check the process ID 1 on your system. Type ps -P 1 to see the process name as follows:

//This Linux is systemd based
$ ps -P 1
  PID PSR TTY      STAT   TIME COMMAND
    1   0 ?        Ss     0:03 /usr/lib/systemd/systemd --switched-root –system

//This Linux is init based
# ps -P 1
  PID PSR TTY      STAT   TIME COMMAND
    1   0 ?        Ss     0:01 /sbin/init

Startup script (systemd)

If you are using systemd-based Linux, such as RHEL 7, CentOS 7, Ubuntu 15.4 or later, you need to prepare the /usr/lib/systemd/system/etcd.service file as follows:

[Unit]
Description=Etcd Server
After=network.target

[Service]
Type=simple
WorkingDirectory=/var/lib/etcd/
EnvironmentFile=/etc/etcd/etcd.conf
User=etcd
ExecStart=/usr/local/bin/etcd

[Install]
WantedBy=multi-user.target

After that, register to systemd using the systemctl command as follows:

# sudo systemctl enable etcd

Then, you restart the system or type sudo systemctl start etcd to launch the etcd daemon. You may check the etcd service status using sudo systemctl status -l etcd.

Startup script (init)

If you are using the init-based Linux, such as Amazon Linux, use the traditional way to prepare the /etc/init.d/etcd script as follows:

#!/bin/bash
#
# etcd This shell script takes care of starting and stopping etcd
#
# chkconfig: - 60 74
# description: etcd

### BEGIN INIT INFO
# Provides: etcd
# Required-Start: $network $local_fs $remote_fs
# Required-Stop: $network $local_fs $remote_fs
# Should-Start: $syslog $named ntpdate
# Should-Stop: $syslog $named
# Short-Description: start and stop etcd
# Description: etcd
### END INIT INFO

# Source function library.
. /etc/init.d/functions

# Source networking configuration.
. /etc/sysconfig/network

prog=/usr/local/bin/etcd
etcd_conf=/etc/etcd/etcd.conf
lockfile=/var/lock/subsys/`basename $prog`
hostname=`hostname`

start() {
  # Start daemon.
. $etcd_conf
  echo -n $"Starting $prog: "
  daemon --user=etcd $prog > /var/log/etcd.log 2>&1 &
  RETVAL=$?
  echo
  [ $RETVAL -eq 0 ] && touch $lockfile
  return $RETVAL
}
stop() {
  [ "$EUID" != "0" ] && exit 4
        echo -n $"Shutting down $prog: "
  killproc $prog
  RETVAL=$?
        echo
  [ $RETVAL -eq 0 ] && rm -f $lockfile
  return $RETVAL
}

# See how we were called.
case "$1" in
  start)
  start
  ;;
  stop)
  stop
  ;;
  status)
  status $prog
  ;;
  restart)
  stop
  start
  ;;
  reload)
  exit 3
  ;;
  *)
  echo $"Usage: $0 {start|stop|status|restart|reload}"
  exit 2
esac

After that, register to init script using the chkconfig command as follows:

//set file permission correctly
$ sudo chmod 755 /etc/init.d/etcd
$ sudo chown root:root /etc/init.d/etcd

//auto start when boot Linux
$ sudo chkconfig --add etcd
$ sudo chkconfig etcd on

Then, you restart the system or type /etc/init.d/etcd start to launch the etcd daemon.

Configuration

There is the file /etc/etcd/etcd.conf to change the configuration of etcd, such as data file path and TCP port number.

The minimal configuration is as follows:

NAME

Mean

Example

Note

ETCD_NAME

Instance name

myhappy-etcd

 

ETCD_DATA_DIR

Data file path

/var/lib/etcd/myhappy.etcd

File path must be owned by etcd user

ETCD_LISTEN_CLIENT_URLS

TCP port number

http://0.0.0.0:8080

Specifying 0.0.0.0, binds all IP address, otherwise use localhost to accept only same machine

ETCD_ADVERTISE_CLIENT_URLS

Advertise this etcd URL to other cluster instances

http://localhost:8080

Use for clustering configuration

Note that you need to use the export directive if you want to use the init-based Linux in order to set environment variables as follows:

$ cat /etc/etcd/etcd.conf

export ETCD_NAME=myhappy-etcd
export ETCD_DATA_DIR="/var/lib/etcd/myhappy.etcd"
export ETCD_LISTEN_CLIENT_URLS="http://0.0.0.0:8080"
export ETCD_ADVERTISE_CLIENT_URLS="http://localhost:8080"

On the other hand, systemd-based Linux doesn't need the export directive as follows:

$ cat /etc/etcd/etcd.conf
ETCD_NAME=myhappy-etcd
ETCD_DATA_DIR="/var/lib/etcd/myhappy.etcd"
ETCD_LISTEN_CLIENT_URLS="http://0.0.0.0:8080"
ETCD_ADVERTISE_CLIENT_URLS="http://localhost:8080"

See also

This section described how to configure etcd. It is easy and simple to operate via the RESTful API, but powerful. However, there's a need to be aware of its security and availability. The following recipes will describe how to ensure that etcd is secure and robust:

  • Exploring architecture
  • The Clustering etcd recipe in Chapter 4, Building a High Availability Cluster
  • The Authentication and authorization recipe in Chapter 7, Advanced Cluster Administration
  • The Working with etcd log recipe in Chapter 8, Logging and Monitoring
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