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post Manual HA Cluster with Linux Containers, DRBD and Btrfs 2014-11-28 19:20 true [HA Clusters Linux Containers DRBD Virtualization IT]

In this post I'm gonna explain you how to deploy really fast and cheap cluster of Linux Containers. I use the same setup in a production enviroment for a big accounting software (10GB++ of MySQL).

{% img center http://petrovs.info/images/lxccluster/diagram1.jpeg Schematic of the setup %}

Why LXC? Because it is Über-cool! Compared to the Hardware Virtualization, the runtime performance is near the bare metal speeds. Operations like starting/stopping of the system or clonning and snapshots are really fast. There's no virtual BIOS, boot loader and kernel. A given number of containers can share the same system resources as they are installed on the same bare metal system and are still isolated. It's really lightweight and flexible. You can containerize everything - a whole system or a single application. Stéphane Graber has a really good blog post series about LXC.

DRBD will provide the block device replication between the servers. Let's think of it as a RAID1 array between the two machines. It can work as master-master or master-slave. The master-master setup is more risky and it works only with shared cluster file systems (GFS, OCFS2 or GlusterFS). I don't have the balls to use it master-master on two nodes for VM's and containers, so in this setup I'll use master-slave. The difference is that when an array is promoted as slave on a given machine, it cannot be accessed.

Btrfs is the new hipster in town :) It's a new "copy on write" file system and logical volume manager for the Linux kernel. It has many similarities with the ZFS, but is part of the kernel. Snapshotting and cloning of the containers are easier with Btrfs. It can make snapshots and subvolumes of a given directory and mount it as another block device. Note that it's already stable but still has problems. Stable filesystem for production environment must be 7+ years old! I bet on the backups :)

So, let's suppose that we have two identical machines with this sample configuration:

  • Intel Xeon E5;
  • 16GB of RAM;
  • 500GB RAID1 array -> /dev/sda;
  • 2x 1TB RAID10 arrays -> /dev/sdb and /dev/sdc;
  • Standart gigabit interface/s -> eth0;
  • 10GB Ethernet interface, linked between the machines -> eth1;

First, install standart Ubuntu LTS on the RAID1 arrays and don't touch the RAID10.

#The Network

The containers will use veth network, so we need to create a bridge:

{% codeblock lang:bash %} sudo apt-get install bridge-utils {% endcodeblock %}

Our internet network will be 10.1.0.0/24 and our peer network - 10.0.254.0/30. So, /etc/network/interfaces of node1 will be:

{% codeblock lang:bash %} auto lo iface lo inet loopback

auto eth0 iface eth0 inet manual

auto br0 iface br0 inet static address 10.1.0.5 netmask 255.255.255.0 gateway 10.1.0.1 #ok, let's put a gateway:) bridge_ports eth0 bridge_fd 0 bridge_stp off bridge_maxwait 0

auto eth1 iface eth1 inet static address 10.0.254.1 netmask 255.255.255.252 {% endcodeblock %}

And for node2:

{% codeblock lang:bash %} auto lo iface lo inet loopback

auto eth0 iface eth0 inet static address 10.1.0.6 netmask 255.255.255.0 gateway 10.1.0.1

auto eth1 iface eth1 inet static address 10.0.254.2 netmask 255.255.255.252 {% endcodeblock %}

... and the hostnames in /etc/hosts. DRBD works with hostnames. On the both machines:

{% codeblock lang:bash %} 127.0.0.1 localhost 10.0.254.1 node1 10.0.254.2 node2 {% endcodeblock %}

{% codeblock lang:bash restart the network %} sudo service networking restart {% endcodeblock %}

#DRBD

Be sure to check the official documentation. The setup of DRBD is really complex and personal, depending on the hardware, the network and the required results.

{% codeblock lang:bash Installing drbd on the both machines %} sudo apt-get install drbd8-utils {% endcodeblock %}

{% codeblock lang:bash Load the kernel module %} sudo apt-get install drbd8-utils {% endcodeblock %}

The time must be in sync for the DRBD. So, install NTP clien:

{% codeblock lang:bash on the both machines %} sudo apt-get install ntp ntpdate {% endcodeblock %}

On this tutorial I will use the whole RAID10 arrays. It would be better if we completely erase the partition tables (if any) and start from scratch with a new partition table and just one, empty partition. Erase the partition tables on the both of the nodes. I expect the drive numbers to be identical because the hardware is the same:

{% codeblock lang:bash %} sudo dd if=/dev/zero of=/dev/sdb bs=1M count=10 sudo dd if=/dev/zero of=/dev/sdc bs=1M count=10 {% endcodeblock %}

DRBD can also be setup in LVM logical volume.

Let's take a look at the partition layout of the drives. For the example in the tutorial, I use a qcow2 image, mounted on my laptop and some information like the disk identifier and model will not appear. Also, sda is not sized for server usage.

{% codeblock lang:bash %} sudo fdisk -l

Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x1f956bec

Device Boot Start End Blocks Id System /dev/sda1 * 2048 409599 203776 7 HPFS/NTFS/exFAT /dev/sda2 409600 646677178 323133789+ 7 HPFS/NTFS/exFAT /dev/sda3 646678526 1464936447 409128961 5 Extended Partition 3 does not start on physical sector boundary. /dev/sda4 1464936448 1465147119 105336 c W95 FAT32 (LBA) /dev/sda5 646678528 689645567 21483520 83 Linux /dev/sda6 689647616 693645311 1998848 82 Linux swap / Solaris /dev/sda7 693647360 1464936447 385644544 83 Linux

Disk /dev/sdb: 1099.5 GB, 1099511627776 bytes 255 heads, 63 sectors/track, 133674 cylinders, total 2147483648 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table

Disk /dev/sdc: 1099.5 GB, 1099511627776 bytes 255 heads, 63 sectors/track, 133674 cylinders, total 2147483648 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000

Disk /dev/sdc doesn't contain a valid partition table

{% endcodeblock %}

To partition the drives, I will use parted. The -a optimal flag will ensure that the partitions are properly aligned.

{% codeblock lang:bash %} sudo parted -a optimal /dev/sdb

GNU Parted 2.3 Using /dev/sdb Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) {% endcodeblock %}

...and create a new partition table:

{% codeblock lang:bash %} (parted) mklabel msdos {% endcodeblock %}

View the available disk space

{% codeblock lang:bash %} (parted) print free Model: Unknown (unknown) Disk /dev/sdb: 1100GB Sector size (logical/physical): 512B/512B Partition Table: msdos

Number Start End Size Type File system Flags 32,3kB 1100GB 1100GB Free Space {% endcodeblock %}

And an overview of the partitions on all drives:

{% codeblock lang:bash %} (parted) print all Model: Unknown (unknown) Disk /dev/sdb: 1100GB Sector size (logical/physical): 512B/512B Partition Table: msdos

Number Start End Size Type File system Flags

Model: Unknown (unknown) Disk /dev/sdc: 1100GB Sector size (logical/physical): 512B/512B Partition Table: msdos

Number Start End Size Type File system Flags

Model: ATA Hitachi HTS54757 (scsi) Disk /dev/sda: 750GB Sector size (logical/physical): 512B/4096B Partition Table: msdos

Number Start End Size Type File system Flags 1 1049kB 210MB 209MB primary ntfs boot 2 210MB 331GB 331GB primary ntfs 3 331GB 750GB 419GB extended 5 331GB 353GB 22,0GB logical ext4 6 353GB 355GB 2047MB logical linux-swap(v1) 7 355GB 750GB 395GB logical ext4 4 750GB 750GB 108MB primary fat32 lba

(parted) {% endcodeblock %}

Create a primary partitions on /dev/sdb and /dev/sdc using all the available disk space. Start at 1049kB, the same block that is used on /dev/sda.

{% codeblock lang:bash %} (parted) mkpart primary 1049kB 1100GB {% endcodeblock %}

And see the new partition:

{% codeblock lang:bash %} (parted) print free
Model: Unknown (unknown) Disk /dev/sdb: 1100GB Sector size (logical/physical): 512B/512B Partition Table: msdos

Number Start End Size Type File system Flags 32,3kB 1049kB 1016kB Free Space 1 1049kB 1100GB 1100GB primary {% endcodeblock %}

Check if the partition is properly aligned:

{% codeblock lang:bash %} (parted) align-check opt 1 {% endcodeblock %}

Backup the default DRBD configuration:

{% codeblock lang:bash %} sudo cp /etc/drbd.conf /root/drbd.conf.back sudo cp /etc/drbd.d/global_common.conf /root/glonal_common.conf.back {% endcodeblock %}

On Ubuntu 14.04, the section "common" is added to /etc/drbd.d/global_common.conf. Add syncer rate:

{% codeblock lang:bash %} global { usage-count no; # minor-count dialog-refresh disable-ip-verification }

common { handlers { # These are EXAMPLE handlers only. # They may have severe implications, # like hard resetting the node under certain circumstances. # Be careful when chosing your poison.

    # pri-on-incon-degr "/usr/lib/drbd/notify-pri-on-incon-degr.sh; /usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ; reboot -f";
	# pri-lost-after-sb "/usr/lib/drbd/notify-pri-lost-after-sb.sh; /usr/lib/drbd/notify-emergency-reboot.sh; echo b > /proc/sysrq-trigger ; reboot -f";
	# local-io-error "/usr/lib/drbd/notify-io-error.sh; /usr/lib/drbd/notify-emergency-shutdown.sh; echo o > /proc/sysrq-trigger ; halt -f";
	# fence-peer "/usr/lib/drbd/crm-fence-peer.sh";
	# split-brain "/usr/lib/drbd/notify-split-brain.sh root";
	# out-of-sync "/usr/lib/drbd/notify-out-of-sync.sh root";
	# before-resync-target "/usr/lib/drbd/snapshot-resync-target-lvm.sh -p 15 -- -c 16k";
	# after-resync-target /usr/lib/drbd/unsnapshot-resync-target-lvm.sh;
}

startup {
	# wfc-timeout degr-wfc-timeout outdated-wfc-timeout wait-after-sb
}

options {
	# cpu-mask on-no-data-accessible
}

disk {
	# size max-bio-bvecs on-io-error fencing disk-barrier disk-flushes
	# disk-drain md-flushes resync-rate resync-after al-extents
            # c-plan-ahead c-delay-target c-fill-target c-max-rate
            # c-min-rate disk-timeout
}

net {
	# protocol timeout max-epoch-size max-buffers unplug-watermark
	# connect-int ping-int sndbuf-size rcvbuf-size ko-count
	# allow-two-primaries cram-hmac-alg shared-secret after-sb-0pri
	# after-sb-1pri after-sb-2pri always-asbp rr-conflict
	# ping-timeout data-integrity-alg tcp-cork on-congestion
	# congestion-fill congestion-extents csums-alg verify-alg
	# use-rle
}

    syncer {
            rate 200M;
    }

} {% endcodeblock %}

The "syncer rate" option is dependable on the hardware and the network. It's necessary to look the official documentation.

And the most important - drbd.conf:

{% codeblock lang:bash %}

You can find an example in /usr/share/doc/drbd.../drbd.conf.example

include "drbd.d/global_common.conf"; include "drbd.d/*.res";

resource r0 { protocol C; startup { wfc-timeout 15; degr-wfc-timeout 60; become-primary-on node1; } net { cram-hmac-alg sha1; shared-secret "super_secret_random_code"; } on node1 { device /dev/drbd0; disk /dev/sdb1; address 10.0.254.1:7788; meta-disk internal; } on node2 { device /dev/drbd0; disk /dev/sdb1; address 10.0.254.2:7788; meta-disk internal; } }

resource r1 { protocol C; startup { wfc-timeout 15; degr-wfc-timeout 60; become-primary-on node1; } net { cram-hmac-alg sha1; shared-secret "another_super_secret_code"; } on node1 { device /dev/drbd1; disk /dev/sdc1; address 10.0.254.1:7789; meta-disk internal; } on node2 { device /dev/drbd2; disk /dev/sdc1; address 10.0.254.2:7789; meta-disk internal; } }

{% endcodeblock %}

Initialize the metadata storage:

{% codeblock lang:bash On both servers %} sudo drbdadm create-md r0 sudo drbdadm create-md r1 {% endcodeblock %}

Start DRBD:

{% codeblock lang:bash On both servers %} sudo /etc/init.d/drbd start {% endcodeblock %}

To start the sync process, make the first server the primary node. Exceute this on the first server only:

{% codeblock lang:bash Only on node1 %} sudo drbdadm -- --overwrite-data-of-peer primary all {% endcodeblock %}

Simmilar to the Linux software raid, you can monitor the process in "/proc/drbd".

After the sync is finnished, promote r1 (/dev/drbd1) to the second node:

{% codeblock lang:bash Only on node 1 %} drbdadm secondary r1 {% endcodeblock %}

{% codeblock lang:bash Only on node 2 %} drbdadm primary r1 {% endcodeblock %}

The DRBD is done, let's setup the Btrfs.

#Btrfs

First, create directories for the mount points:

{% codeblock lang:bash On both servers %} mkdir /srv/{store1,store2} {% endcodeblock %}

Install Btrfs

{% codeblock lang:bash On both servers %} sudo apt-get install btrfs-tools {% endcodeblock %}

{% codeblock lang:bash Only on node 1 %} sudo mkfs.btrfs /dev/drbd0 mount /dev/drbd0 /srv/store1 {% endcodeblock %}

{% codeblock lang:bash Only on node 2 %} sudo mkfs.btrfs /dev/drbd1 mount /dev/drbd1 /dev/store2 {% endcodeblock %}

Let's see the available space:

{% codeblock lang:bash Only on node 1 %} du -h /srv/store1 Filesystem Size Used Avail Use% Mounted on /dev/drbd0 1,0T 384K 1023G 1% /srv/store1 {% endcodeblock %}

It would be identical on node2.

Ok, it's time for the Lxc.

#LXC

{% codeblock lang:bash On both servers %} sudo apt-get install lxc {% endcodeblock %}

Create directories for the containers:

{% codeblock lang:bash Only on node 1 %} mkdir /srv/store1/containers {% endcodeblock %}

{% codeblock lang:bash Only on node 2 %} mkdir /srv/store2/containers {% endcodeblock %}

Change the default path in /etc/lxc.conf. The file may doesn't exist:

{% codeblock lang:bash Only on node 1 %} lxc.lxcpath = /srv/store1/containers {% endcodeblock %}

{% codeblock lang:bash Only on node 2 %} lxc.lxcpath = /srv/store2/containers {% endcodeblock %}

Change the default veth network to br0 in /etc/lxc/default.conf:

{% codeblock lang:bash On both servers %} lxc.betwork.type = veth lxc.network.link = br0 lxc.network.flags = up lxc.network.hwaddr = 00:16:3e:xx:xx:xx {% endcodeblock %}

#Tests

The system should be ready for production. Let's create the first template. In Node1, for example:

{% codeblock lang:bash Only on node 1 %} lxc-create -t ubuntu -n mysql -B btrfs {% endcodeblock %}

Without "-b btrfs", the container's backing store will be treated as a filesystem directory and the snapshots and clones will be created with simple file copy.

Copy with scp the files /srv/store1/containers/mysql/config and /srv/store1/containers/mysql/fstab to the according directory in node2 - */srv/store2/containers/mysql/ . This is necessary for the failover setup. If, for example, node1 fails, the container "mysql" will be easily run from node2 if the /dev/drbd0 is promoted as a primary there:

{% codeblock lang:bash %} drbdadm primary r1 mount /dev/drbd0 /srv/store1 lxc-start -n mysql -d {% endcodeblock %}

##Snapshot can be created with:

{% codeblock lang:bash %} lxc-snapshot -n mysql lxc-snapshot -n mysql -L #will list the snapshots lxc-snapshot -n mysql -d snap0 # will delete snap0 {% endcodeblock %}

There is a lot of documentation available about the LXC commands and configuration options. I'll post a small howto anyway. I'm still writing backup scripts with the LXC api. If they are done, I'll post documentation about the backup.