First of all, a bit of background and why I love the cloud. Previously, I have worked for large ISP's (UUNet, Level 3, British Telecom) and a couple of startups. In some cases, when I'd provision a new system, I'd go to the vendor website, spec out the box, order it, wait for it to arrive, rack and console it. Then, I'd provision switch ports, etc and through an OS and apps on it. Then, I'd unrack it, box it up and drive it to the data center. Re-rack, cable, test, switch port configure it, etc. Took a huge amount of effort. With ec2 and cloud computing, you run a few commands and you're up and running in like, oh.. 20 minutes or so. So, that's awesome, convenient, etc.
You can either run a public AMI, an image created by some random person, or you can build and run you're own. Here's how to do it my way.
First a couple of assumptions, you're running this sequence on an existing CentOS system. You have the fuse module loaded:
modprobe fuse && lsmod | grep fuseNeed that to do loopback mounts.
Ok, let's get started. Note that this whole thing can be scripted but I figured I'd give a little explanation on each step.
So, first let's create a directory to work in:
mkdir -p ~/ami/centos/ && cd ~/ami/
Now, we're going to create an empty disk image. If you know about anaconda, this is just like the downloading stage2 process (well, kinda). Mine is going to be 2G because I like to have a bunch of stuff in there. Change count to 1024 if you want it to be smaller.
dd if=/dev/zero of=centos.fs bs=1M count=2048
Now, create a file system on it:
mke2fs -F -j centos.fs
Good, now we're going to open it up to be written to by mounting it:
mount -o loop centos.fs ~/ami/centos/
Ok, now we're going to turn this thing into a Linux system you can boot up. The kernel likes to have this stuff. The directory ~/ami/centos/ is the root directory / on your new instance.
Make the /dev/ directory:
mkdir ~/ami/centos/dev /sbin/MAKEDEV -d ~/ami/centos/dev/ -x console /sbin/MAKEDEV -d ~/ami/centos/dev/ -x null /sbin/MAKEDEV -d ~/ami/centos/dev/ -x zero
Now, we're going to use yum - just the way the default installer does to add a bunch of software to your new system. We create a yum.conf on the local file system to use to install OS and software.
Add this to the file:
[main] cachedir=/var/cache/yum debuglevel=2 logfile=/var/log/yum.log exclude=*-debuginfo gpgcheck=0 obsoletes=1 pkgpolicy=newest distroverpkg=redhat-release tolerant=1 exactarch=1 reposdir=/dev/null metadata_expire=1800 [base] name=CentOS-5.5 Base baseurl=http://mirror.centos.org/centos/5.5/os/x86_64/ gpgcheck=0 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5.5 priority=1 protect=1 #released updates [update] name=CentOS-5.5 Updates baseurl=http://mirror.centos.org/centos/5.5/updates/x86_64/ gpgcheck=0 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5.5 priority=1 protect=1 #packages used/produced in the build but not released [addons] name=CentOS-5.5 Addons baseurl=http://mirror.centos.org/centos/5.5/addons/x86_64/ gpgcheck=0 gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos5.5 priority=1 [extras] name=CentOS 5.5 Extras $releasever $basearch baseurl=http://mirror.centos.org/centos/5.5/extras/x86_64/ enabled=1
So that pulls stuff from the official CentOS mirror list. GPG checking is off because we don't have the keys installed.
Next, create the proc file system and mount it up. This is where the kernel keeps track of all the stuff it's doing.
mkdir ~/ami/centos/proc mount -t proc none ~/ami/centos/proc/
Ok, here's where the magic begins to happen. We're going to start loading os packages:
yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall Core
So using that command, you can install all the stuff you want. The following is my list, you probably don't need the group 'Development Tools'. That's a BUNCH of stuff you only really need if you're doing development. I like to have it on some instances, some it never gets used. So, you should probably ignore it. A good way to see what's available to install is to run:
yum grouplist | less
and that'll tell you what package groups exist. If you're creating a DNS server, you'll want to add the 'DNS Name Server' group. Pick through the list below and install what you want/need. Not everybody is going to want JDK for example.
yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall 'Text-based Internet' yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall Ruby yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall 'Web Server' yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall 'Development Tools' yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall 'Java' yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y groupinstall 'MySQL Database' yum -c ~/ami/yum.conf --installroot=/root/ami/centos -y install curl wget rsync sudo mlocate lsof man tcpdump bc iptables
Once all your software is installed, configure sshd. Now, this is just an old sysadmin tip. Don't run sshd on port 22. It gets scanned 24x7x365 with all kinds of brute force attacks and everything else. I always, always, always run it on another port. You can do tcpwrappers and other tricks (iptables, etc) but just running it on some higher port saves you tons of problems.
So, in this example, I'm running on port 55000.
and add something like this:
Port 55000 Protocol 2 SyslogFacility AUTHPRIV PermitRootLogin yes MaxAuthTries 4 PasswordAuthentication no ChallengeResponseAuthentication no GSSAPIAuthentication yes GSSAPICleanupCredentials yes UsePAM yes AcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES AcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT AcceptEnv LC_IDENTIFICATION LC_ALL X11Forwarding yes Subsystem sftp /usr/libexec/openssh/sftp-server
Create a resolv.conf file with valid name servers. I pretty much always use google's because it's fast and anycasted so it's going to be fast no matter where you are, and it's google.
# Google's public DNS servers. nameserver 220.127.116.11 nameserver 18.104.22.168
Now, configure you motd. This is the banner that gets displayed whenever anyone logs in:
Put whatever you want in there.. here's an example:
________________________________________ / Unauthorized users will be killed and \ \ eaten. / ---------------------------------------- \ ^__^ \ (xx)\_______ (__)\ )\/\ U ||----w | || ||
This is optional too but I like to have ec2tools installed on my instances:
cd ~/ami/centos/ && wget http://s3.amazonaws.com/ec2-downloads/ec2-ami-tools.noarch.rpm* chroot /root/ami/centos rpm -Uvh ec2-ami-tools.noarch.rpm
export EC2_HOME=/opt/ec2-tools export PATH=$EC2_HOME/bin:$PATH
Now, configure DHCP for networking:
mkdir -p /etc/sysconfig/network-scripts/ vi /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0 BOOTPROTO=dhcp ONBOOT=yes TYPE=Ethernet USERCTL=yes PEERDNS=yes IPV6INIT=no PERSISTENT_DHCLIENT=yes
That PERSISTENT_DHCLIENT is very nice to have. It means that if for some reason the DHCP server bites the dust, keep the lease you have. Otherwise your instance could loose it's IP at which point, it's game over.
Turn on networking:
Now, configure fstab to mount everything up:
Add the following:
/dev/sda1 / ext3 defaults 1 1 none /dev/pts devpts gid=5,mode=620 0 0 none /dev/shm tmpfs defaults 0 0 none /proc proc defaults 0 0 none /sys sysfs defaults 0 0 /dev/sdc1 /mnt ext3 defaults 0 0 /dev/sdc2 swap swap defaults 0 0
Next, turn on the services you want.
chroot ~/ami/centos/ bash chkconfig --level 345 sshd on chkconfig --level 345 httpd on exit
Almost done. I also like to add a user account with a password and sudo access, so if for some reason I can't get in with my ssh key(s), I can just login as this user and sudo to root and figure out what's going on. This step is optional but very useful:
chroot ~/ami/centos/ bash useradd -g users mclovin passwd mclovin
Then add your user to the sudoers file:
find this line:
root ALL=(ALL) ALL
and add your new user:
mclovin ALL=(ALL) ALL
Then, exit the chroot'd env:
That's pretty much it holmes. Once that's all done you can unmount the image file. Bundle, upload and run.