Wed 26 Sep 2012
Tags: devops, sysadmin.
If you're a modern sysadmin you've probably been sipping at the devops
koolaid and trying out one or more of the current system configuration
management tools like puppet or chef.
These tools are awesome - particularly for homogenous large-scale
deployments of identical nodes.
In practice in the enterprise, though, things get more messy. You can
have legacy nodes that can't be puppetised due to their sensitivity and
importance; or nodes that are sufficiently unusual that the payoff of
putting them under configuration management doesn't justify the work;
or just systems which you don't have full control over.
We've been using a simple tool called extract in these kinds of
environments, which pulls a given set of files from remote hosts and
stores them under version control in a set of local per-host trees.
You can think of it as the yang to puppet or chef's yin - instead of
pushing configs onto remote nodes, it's about pulling configs off
nodes, and storing them for tracking and change control.
We've been primarily using it in a RedHat/CentOS environment, so we
use it in conjunction with
rpm-find-changes,
which identifies all the config files under /etc that have been
changed from their deployment versions, or are custom files not
belonging to a package.
Extract doesn't care where its list of files to extract comes from, so
it should be easily customised for other environments.
It uses a simple extract.conf shell-variable-style config file,
like this:
# Where extracted files are to be stored (in per-host trees)
EXTRACT_ROOT=/data/extract
# Hosts from which to extract (space separated)
EXTRACT_HOSTS=host1 host2 host3
# File containing list of files to extract (on the remote host, not locally)
EXTRACT_FILES_REMOTE=/var/cache/rpm-find-changes/etc.txt
Extract also allows arbitrary scripts to be called at the beginning
(setup) and end (teardown) of a run, and before and/or after each host.
Extract ships with some example shell scripts for loading ssh keys, and
checking extracted changes into git or bzr. These hooks are also
configured in the extract.conf config e.g.:
# Pre-process scripts
# PRE_EXTRACT_SETUP - run once only, before any extracts are done
PRE_EXTRACT_SETUP=pre_extract_load_ssh_keys
# PRE_EXTRACT_HOST - run before each host extraction
#PRE_EXTRACT_HOST=pre_extract_noop
# Post process scripts
# POST_EXTRACT_HOST - run after each host extraction
POST_EXTRACT_HOST=post_extract_git
# POST_EXTRACT_TEARDOWN - run once only, after all extracts are completed
#POST_EXTRACT_TEARDOWN=post_extract_touch
Extract is available on github, and
packages for RHEL/CentOS 5 and 6 are available from
my repository.
Feedback/pull requests always welcome.
Fri 28 Oct 2011
Tags: centos, ldap, linux, openldap, rhel, sysadmin.
Having spent too much of this week debugging problems around migrating
ldap servers from RHEL5 to RHEL6, here are some miscellaneous notes
to self:
The service is named ldap on RHEL5, and slapd on RHEL6 e.g.
you do service ldap start on RHEL5, but service slapd start
on RHEL6
On RHEL6, you want all of the following packages installed on your clients:
yum install openldap-clients pam_ldap nss-pam-ldapd
This seems to be the magic incantation that works for me (with real SSL
certificates, though):
authconfig --enableldap --enableldapauth \
--ldapserver ldap.example.com \
--ldapbasedn="dc=example,dc=com" \
--update
Be aware that there are multiple ldap configuration files involved now.
All of the following end up with ldap config entries in them and need to
be checked:
- /etc/openldap/ldap.conf
- /etc/pam_ldap.conf
- /etc/nslcd.conf
- /etc/sssd/sssd.conf
Note too that /etc/openldap/ldap.conf uses uppercased directives (e.g. URI)
that get lowercased in the other files (URI -> uri). Additionally, some
directives are confusingly renamed as well - e.g. TLA_CACERT in
/etc/openldap/ldap.conf becomes tla_cacertfile in most of the others.
:-(
If you want to do SSL or TLS, you should know that the default behaviour
is for ldap clients to verify certificates, and give misleading bind errors
if they can't validate them. This means:
if you're using self-signed certificates, add TLS_REQCERT allow to
/etc/openldap/ldap.conf on your clients, which means allow certificates
the clients can't validate
if you're using CA-signed certificates, and want to verify them, add
your CA PEM certificate to a directory of your choice (e.g.
/etc/openldap/certs, or /etc/pki/tls/certs, for instance), and point
to it using TLA_CACERT in /etc/openldap/ldap.conf, and
tla_cacertfile in /etc/ldap.conf.
RHEL6 uses a new-fangled /etc/openldap/slapd.d directory for the old
/etc/openldap/slapd.conf config data, and the
RHEL6 Migration Guide
tells you to how to convert from one to the other. But if you simply
rename the default slapd.d directory, slapd will use the old-style
slapd.conf file quite happily, which is much easier to read/modify/debug,
at least while you're getting things working.
If you run into problems on the server, there are lots of helpful utilities
included with the openldap-servers package. Check out the manpages for
slaptest(8), slapcat(8), slapacl(8), slapadd(8), etc.
Further reading:
Tue 18 Oct 2011
Tags: centos, linux, rhel, sysadmin.
rpm-find-changes is a little script I wrote a while ago for rpm-based
systems (RedHat, CentOS, Mandriva, etc.). It finds files in a filesystem
tree that are not owned by any rpm package (orphans), or are modified
from the version distributed with their rpm. In other words, any file
that has been introduced or changed from it's distributed version.
It's intended to help identify candidates for backup, or just for
tracking interesting changes. I run it nightly on /etc on most of my
machines, producing a list of files that I copy off the machine (using
another tool, which I'll blog about later) and store in a git
repository.
I've also used it for tracking changes to critical configuration trees
across multiple machines, to make sure everything is kept in sync, and
to be able to track changes over time.
Available on github:
https://github.com/gavincarr/rpm-find-changes
Wed 23 Feb 2011
Tags: redis, ruby, sysadmin.
When you have more than a handful of hosts on your network, you need to
start keeping track of what services are living where, what roles
particular servers have, etc. This can be documentation-based (say on a
wiki, or offline), or it can be implicit in a configuration management
system. Old-school sysadmins often used dns TXT records for these kind of
notes, on the basis that it was easy to look them up from the command
line from anywhere.
I've been experimenting with the idea of using lightweight tags attached
to hostnames for this kind of data, and it's been working really nicely.
Hosttag is just a couple of ruby command line utilities, one (hosttag
or ht) for doing tag or host lookups, and one (htset/htdel) for
doing adds and deletes. Both are network based, so you can do lookups
from wherever you are, rather than having to go to somewhere centralised.
Hosttag uses a redis server to store the hostname-tag
and tag-hostname mappings as redis sets, which makes queries lightning
fast, and setup straightforward.
So let's see it in action (rpms available in
my yum repo):
# Installation - first install redis somewhere, and setup a 'hosttag'
# dns alias to the redis host (or use the `-s <server>` option in
# the examples that follow). e.g. on CentOS:
$ yum install redis rubygem-redis
# Install hosttag as an rpm package (from my yum repo).
# Also requires/installs the redis rubygem.
$ yum install hosttag
# gem version coming soon (gem install hosttag)
# Setup some test data (sudo is required for setting and deleting)
# Usage: htset --tag <host> <tag1> <tag2> <tag3> ...
$ sudo htset --tag server1 dns dell ldap server centos centos5 i386 syd
$ sudo htset --tag server2 dns dell ldap server debian debian6 x86_64 mel
$ sudo htset --tag server3 hp nfs server centos centos6 x86_64 syd
$ sudo htset --tag lappy laptop ubuntu maverick i386 syd
# Now run some queries
# Query by tag
$ ht dns
server1 server2
$ ht i386
lappy server1
# Query by host
$ ht server2
debian debian6 dell dns ldap mel server x86_64
# Multiple arguments
$ ht --or centos debian
server1 server2 server3
$ ht --and dns ldap
server1 server2
# All hosts
$ ht --all
lappy server1 server2 server3
# All tags
$ ht --all-tags
centos centos5 centos6 debian debian6 dell dns hp i386 laptop ldap \
maverick mel nfs server syd ubuntu x86_64
An obvious use case is to perform actions on multiple hosts using your
ssh loop of choice e.g.
$ sshr $(ht centos) 'yum -y update'
Finally, a warning: hosttag doesn't have any security built in yet, so it
should only be used on trusted networks.
Source code is on github: https://github.com/gavincarr/hosttag - patches
welcome :-).
Sun 09 Jan 2011
Tags: linux, sysadmin.
Here's what I use to take a quick inventory of a machine before a rebuild,
both to act as a reference during the rebuild itself, and in case something
goes pear-shaped. The whole chunk after script up to exit is
cut-and-pastable.
# as root, where you want your inventory file
script $(hostname).inventory
export PS1='\h:\w\$ ' # reset prompt to avoid ctrl chars
fdisk -l /dev/sd? # list partition tables
cat /proc/mdstat # list raid devices
pvs # list lvm stuff
vgs
lvs
df -h # list mounts
ip addr # list network interfaces
ip route # list network routes
cat /etc/resolv.conf # show resolv.conf
exit
# Cleanup control characters in the inventory
perl -i -pe 's/\r//g; s/\033\]\d+;//g; s/\033\[\d+m//g; s/\007/\//g' \
$(hostname).inventory
# And then copy it somewhere else in case of problems ;-)
scp $(hostname).inventory somewhere:
Anything else useful I've missed?
Sat 04 Dec 2010
Tags: blosxom, cronologue, sysadmin.
Came across cronologger
(blog post)
recently (via Dean Wilson),
which is a simple wrapper script you use around your cron(8) jobs, which
captures any stdout and stderr output and logs it to a couchdb database,
instead of the traditional behaviour of sending it to you as email.
It's a nice idea, particularly for jobs with important output where it
would be nice to able to look back in time more easily than by trawling
through a noisy inbox, or for sites with lots of cron jobs where the sheer
volume is difficult to handle usefully as email.
Cronologger comes with a simple web interface for displaying your cron jobs,
but so far it's pretty rudimentary. I quickly realised that this was another
place (cf. blosxom4nagios) where
blosxom could be used to provide a pretty
useful gui with very little work.
Thus: cronologue.
cronologue(1) is the wrapper, written in perl, which logs job records and
and stdout/stderr output via standard HTTP PUTs back to a designated apache
server, as flat text files. Parameters can be used to control whether job
records are always created, or only when there is output produced. There's
also a --passthru mode in which stdout and stderr streams are still output,
allowing both email and cronologue output to be produced.
On the server side a custom blosxom install is used to display the job records,
which can be filtered by hostname or by date. There's also an RSS feed available.
Obligatory screenshot:
Update: I should add that RPMs for CentOS5 (but which will probably work on
most RPM-based distros) are available from
my yum repository.
Tue 16 Nov 2010
Tags: brackup, centos, rhel, riak, sysadmin.
Been playing with Riak recently, which is
one of the modern dynamo-derived nosql databases (the other main ones being
Cassandra and Voldemort). We're evaluating it for use as a really large
brackup datastore, the primary attraction
being the near linear scalability available by adding (relatively cheap) new
nodes to the cluster, and decent availability options in the face of node
failures.
I've built riak packages for RHEL/CentOS 5, available at my
repository,
and added support for a riak 'target' to the latest
version (1.10) of brackup (packages
also available at my repo).
The first thing to figure out is the maximum number of nodes you expect
your riak cluster to get to. This you use to size the ring_creation_size
setting, which is the number of partitions the hash space is divided into.
It must be a power of 2 (64, 128, 256, etc.), and the reason it's important
is that it cannot be easily changed after the cluster has been created.
The rule of thumb is that for performance you want at least 10 partitions
per node/machine, so the default ring_creation_size of 64 is really only
useful up to about 6 nodes. 128 scales to 10-12, 256 to 20-25, etc. For more
info see the Riak Wiki.
Here's the script I use for configuring a new node on CentOS. The main
things to tweak here are the ring_creation_size you want (here I'm using
512, for a biggish cluster), and the interface to use to get the default ip
address (here eth0, or you could just hardcode 0.0.0.0 instead of $ip).
#!/bin/sh
# Riak configuration script for CentOS/RHEL
# Install riak (and IO::Interface, for next)
yum -y install riak perl-IO-Interface
# To set app.config:web_ip to use primary ip, do:
perl -MIO::Interface::Simple -i \
-pe "BEGIN { \$ip = IO::Interface::Simple->new(q/eth0/)->address; }
s/127\.0\.0\.1/\$ip/" /etc/riak/app.config
# To add a ring_creation_size clause to app.config, do:
perl -i \
-pe 's/^((\s*)%% riak_web_ip)/$2%% ring_creation_size is the no. of partitions to divide the hash
$2%% space into (default: 64).
$2\{ring_creation_size, 512\},
$1/' /etc/riak/app.config
# To set riak vm_args:name to hostname do:
perl -MSys::Hostname -i -pe 's/127\.0\.0\.1/hostname/e' /etc/riak/vm.args
# display (bits of) config files for checking
echo
echo '********************'
echo /etc/riak/app.config
echo '********************'
head -n30 /etc/riak/app.config
echo
echo '********************'
echo /etc/riak/vm.args
echo '********************'
cat /etc/riak/vm.args
Save this to a file called e.g. riak_configure, and then to configure a couple
of nodes you do the following (note that NODE is any old internal hostname you use
to ssh to the host in question, but FIRST_NODE needs to use the actual -name
parameter defined in /etc/riak/vm.args on your first node):
# First node
NODE=node1
cat riak_configure | ssh $NODE sh
ssh $NODE 'chkconfig riak on; service riak start'
# Run the following until ringready reports TRUE
ssh $NODE riak-admin ringready
# All nodes after the first
FIRST_NODE=riak@node1.example.com
NODE=node2
cat riak_configure | ssh $NODE sh
ssh $NODE "chkconfig riak on; service riak start && riak-admin join $FIRST_NODE"
# Run the following until ringready reports TRUE
ssh $NODE riak-admin ringready
That's it. You should now have a working riak cluster accessible on port 8098 on your
cluster nodes.
Fri 08 Oct 2010
Tags: centos, pxe, sysadmin.
Problem: you've got a remote server that's significantly hosed, either
through a screwup somewhere or a power outage that did nasty things to
your root filesystem or something. You have no available remote hands,
and/or no boot media anyway.
Preconditions: You have another server you can access on the same
network segment, and remote access to the broken server, either through
a DRAC or iLO type card, or through some kind of serial console server
(like a Cyclades/Avocent box).
Solution: in extremis, you can do a remote rebuild. Here's the simplest
recipe I've come up with. I'm rebuilding using centos5-x86_64 version
5.5; adjust as necessary.
Note: dnsmasq, mrepo and syslinux are not core CentOS packages,
so you need to enable the rpmforge
repository to follow this recipe. This just involves:
wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.1-1.el5.rf.x86_64.rpm
rpm -Uvh rpmforge-release-0.5.1-1.el5.rf.x86_64.rpm
1. On your working box (which you're now going to press into service as a
build server), install and configure dnsmasq
to provide dhcp and tftp services:
# Install dnsmasq
yum install dnsmasq
# Add the following lines to the bottom of your /etc/dnsmasq.conf file
# Note that we don't use the following ip address, but the directive
# itself is required for dnsmasq to turn dhcp functionality on
dhcp-range=ignore,192.168.1.99,192.168.1.99
# Here use the broken server's mac addr, hostname, and ip address
dhcp-host=00:d0:68:09:19:80,broken.example.com,192.168.1.5,net:centos5x
# Point the centos5x tag at the tftpboot environment you're going to setup
dhcp-boot=net:centos5x,/centos5x-x86_64/pxelinux.0
# And enable tftp
enable-tftp
tftp-root = /tftpboot
#log-dhcp
# Then start up dnsmasq
service dnsmasq start
2. Install and configure mrepo
to provide your CentOS build environment:
# Install mrepo and syslinux
yum install mrepo syslinux
# Setup a minimal /etc/mrepo.conf e.g.
cat > /etc/mrepo.conf
[main]
srcdir = /var/mrepo
wwwdir = /var/www/mrepo
confdir = /etc/mrepo.conf.d
arch = x86_64
mailto = root@example.com
smtp-server = localhost
pxelinux = /usr/lib/syslinux/pxelinux.0
tftpdir = /tftpboot
[centos5]
release = 5
arch = x86_64
metadata = repomd repoview
name = Centos-$release $arch
#iso = CentOS-$release.5-$arch-bin-DVD-?of2.iso
#iso = CentOS-$release.5-$arch-bin-?of8.iso
^D
# (uncomment one of the iso lines above, either the DVD or the CD one)
# Download the set of DVD or CD ISOs for the CentOS version you want
# There are fewer DVD ISOs, but you need to use bittorrent to download
mkdir -p /var/mrepo/iso
cd /var/mrepo/iso
elinks http://isoredirect.centos.org/centos/5.5/isos/x86_64/
# Once your ISOs are available in /var/mrepo/iso, and the 'iso' line
# in /etc/mrepo.conf updated appropriately, run mrepo itself
mrepo -gvv
3. Finally, finish setting up your tftp environment. mrepo should have copied
appropriate pxelinux.0, initrd.img, and vmlinuz files into your
/tftpboot/centos5-x86_64 directory, so all you need to supply is an
appropriate grub boot config:
cd /tftpboot/centos5-x86_64
ls
mkdir -p pxelinux.cfg
# Setup a default grub config (adjust the serial/console and repo params as needed)
cat > pxelinux.cfg/default
default linux
serial 0,9600n8
label linux
root (nd)
kernel vmlinuz
append initrd=initrd.img console=ttyS0,9600 repo=http://192.168.1.1/mrepo/centos5-x86_64
^D
Now get your server to do a PXE boot (via a boot option or the bios or whatever),
and hopefully your broken server will find your dhcp/tftp environment and boot up
in install mode, and away you go.
If you have problems with the boot, try checking your /var/log/messages file on the
boot server for hints.
Mon 22 Mar 2010
Tags: centos, dell, linux, omsa, rhel, sysadmin.
Following on from my IPMI explorations, here's the next
chapter in my getting-down-and-dirty-with-dell-hardware-on-linux adventures.
This time I'm setting up Dell's
OpenManage Server Administrator
software, primarily in order to explore being able to configure bios settings
from within the OS. As before, I'm running CentOS 5, but OMSA supports any of
RHEL4, RHEL5, SLES9, and SLES10, and various versions of Fedora Core and
OpenSUSE.
Here's what I did to get up and running:
# Configure the Dell OMSA repository
wget -O bootstrap.sh http://linux.dell.com/repo/hardware/latest/bootstrap.cgi
# Review the script to make sure you trust it, and then run it
sh bootstrap.sh
# OR, for CentOS5/RHEL5 x86_64 you can just install the following:
rpm -Uvh http://linux.dell.com/repo/hardware/latest/platform_independent/rh50_64/prereq/\
dell-omsa-repository-2-5.noarch.rpm
# Install base version of OMSA, without gui (install srvadmin-all for more)
yum install srvadmin-base
# One of daemons requires /usr/bin/lockfile, so make sure you've got procmail installed
yum install procmail
# If you're running an x86_64 OS, there are a couple of additional 32-bit
# libraries you need that aren't dependencies in the RPMs
yum install compat-libstdc++-33-3.2.3-61.i386 pam.i386
# Start OMSA daemons
for i in instsvcdrv dataeng dsm_om_shrsvc; do service $i start; done
# Finally, you can update your path by doing logout/login, or just run:
. /etc/profile.d/srvadmin-path.sh
Now to check whether you're actually functional you can try a few of the
following (as root):
omconfig about
omreport about
omreport system -?
omreport chassis -?
omreport is the OMSA CLI reporting/query tool, and omconfig is the
equivalent update tool. The main documentation for the current version of
OMSA is here.
I found the CLI User's Guide
the most useful.
Here's a sampler of interesting things to try:
# Report system overview
omreport chassis
# Report system summary info (OS, CPUs, memory, PCIe slots, DRAC cards, NICs)
omreport system summary
# Report bios settings
omreport chassis biossetup
# Fan info
omreport chassis fans
# Temperature info
omreport chassis temps
# CPU info
omreport chassis processors
# Memory and memory slot info
omreport chassis memory
# Power supply info
omreport chassis pwrsupplies
# Detailed PCIe slot info
omreport chassis slots
# DRAC card info
omreport chassis remoteaccess
omconfig allows setting object attributes using a key=value syntax, which
can get reasonably complex. See the CLI User's Guide above for details, but
here are some examples of messing with various bios settings:
# See available attributes and settings
omconfig chassis biossetup -?
# Turn the AC Power Recovery setting to On
omconfig chassis biossetup attribute=acpwrrecovery setting=on
# Change the serial communications setting (on with serial redirection via)
omconfig chassis biossetup attribute=serialcom setting=com1
omconfig chassis biossetup attribute=serialcom setting=com2
# Change the external serial connector
omconfig chassis biossetup attribute=extserial setting=com1
omconfig chassis biossetup attribute=extserial setting=rad
# Change the Console Redirect After Boot (crab) setting
omconfig chassis biossetup attribute=crab setting=enabled
omconfig chassis biossetup attribute=crab setting=disabled
# Change NIC settings (turn on PXE on NIC1)
omconfig chassis biossetup attribute=nic1 setting=enabledwithpxe
Finally, there are some interesting formatting options available to both
omreport, for use in scripting e.g.
# Custom delimiter format (default semicolon)
omreport chassis -fmt cdv
# XML format
omreport chassis -fmt xml
# To change the default cdv delimiter
omconfig preferences cdvformat -?
omconfig preferences cdvformat delimiter=pipe
Wed 20 Jan 2010
Tags: backups, brackup, sysadmin.
After using brackup for a while you find
you have a big list of backups sitting on your server, and start to think
about cleaning up some of the older ones. The standard brackup tool for this
is brackup-target, and the prune and gc (garbage collection)
subcommands.
Typical usage is something like this:
# List the backups for a particular target on the server e.g.
TARGET=myserver_images
brackup-target $TARGET list-backups
Backup File Backup Date Size (B)
----------- ----------- --------
images-1262106544 Thu 31 Dec 2009 03:32:49 1263128
images-1260632447 Sun 13 Dec 2009 08:19:13 1168281
images-1250042378 Wed 25 Nov 2009 06:25:06 977464
images-1239323644 Mon 09 Nov 2009 00:30:34 846523
images-1239577352 Thu 29 Oct 2009 13:03:02 846523
...
# Decide how many backups you want to keep, and prune (delete) the rest
brackup-target --keep-backups 15 $TARGET prune
# Prune just removes the brackup files on the server, so now you need to
# run a garbage collect to delete any 'chunks' that are now orphaned
brackup-target --interactive $TARGET gc
This simple scheme - "keep the last N backups" - works pretty nicely for
backups you do relatively infrequently. If you do more frequent backups,
however, you might find yourself wanting to be able to implement more
sophisticated retention policies. Traditional backup regimes often involve
policies like this:
- keep the last 2 weeks of daily backups
- keep the last 8 weekly backups
- keep monthly backups forever
It's not necessarily obvious how to do something like this with brackup, but
it's actually pretty straightforward. The trick is to define multiple
'sources' in your brackup.conf, one for each backup 'level' you want to use.
For instance, to implement the regime above, you might define the following:
# Daily backups
[SOURCE:images]
path = /data/images
...
# Weekly backups
[SOURCE:images-weekly]
path = /data/images
...
# Monthly backups
[SOURCE:images-monthly]
path = /data/images
...
You'd then use the images-monthly source once a month, the images-weekly
source once a week, and the images source the rest of the time. Your list
of backups would then look something like this:
Backup File Backup Date Size (B)
----------- ----------- --------
images-1234567899 Sat 05 Dec 2009 03:32:49 1263128
images-1234567898 Fri 04 Dec 2009 03:19:13 1168281
images-1234567897 Thu 03 Dec 2009 03:19:13 1168281
images-1234567896 Wed 02 Dec 2009 03:19:13 1168281
images-monthly-1234567895 Tue 01 Dec 2009 03:19:13 1168281
images-1234567894 Mon 30 Nov 2009 03:19:13 1168281
images-weekly-1234567893 Sun 29 Nov 2009 03:19:13 1168281
images-1234567892 Sat 28 Nov 2009 03:25:06 977464
...
And when you prune, you want to specify a --source argument, and specify
separate --keep-backups settings for each level e.g. for the above:
# Keep 2 weeks worth of daily backups
brackup-target --source images --keep-backups 12 $TARGET prune
# Keep 8 weeks worth of weekly backups
brackup-target --source images-weekly --keep-backups 8 $TARGET prune
# Keep all monthly backups, so we don't prune them at all
# And then garbage collect as normal
brackup-target --interactive $TARGET gc
Fri 01 Jan 2010
Tags: anycast, dns, linux, sysadmin.
(Okay, brand new year - must be time to get back on the blogging wagon ...)
Linux Journal recently had a really good article
by Philip Martin on Anycast DNS. It's
well worth a read - I just want to point it out and record a cutdown version of
how I've been setting it up recently.
As the super-quick intro, anycast is the idea of providing a network service
at multiple points in a network, and then routing requests to the 'nearest'
service provider for any particular client. There's a one-to-many relationship
between an ip address and the hosts that are providing services on that address.
In the LJ article above, this means you provide a service on a /32 host address,
and then use a(n) (interior) dynamic routing protocol to advertise that address
to your internal routers. If you're a non-cisco linux shop, that means using
quagga/ospf.
The classic anycast service is dns, since it's stateless and benefits from the
high availability and low latency benefits of a distributed anycast service.
So here's my quick-and-dirty notes on setting up an anycast dns server on
CentOS/RHEL using dnsmasq for dns, and quagga zebra/ospfd for the routing.
First, setup your anycast ip address (e.g. 192.168.255.1/32) on a random
virtual loopback interface e.g. lo:0. On CentOS/RHEL, this means you want
to setup a /etc/sysconfig/network-scripts/ifcfg-lo:0 file containing:
DEVICE=lo:0
IPADDR=192.168.255.1
NETMASK=255.255.255.255
ONBOOT=yes
Setup your dns server to listen to (at least) your anycast dns interface.
With dnsmasq, I use an /etc/dnsmasq.conf config like:
interface=lo:0
domain=example.com
local=/example.com/
resolv.conf=/etc/resolv.conf.upstream
expand-hosts
domain-needed
bogus-priv
Use quagga's zebra/ospfd to advertise this host address to your internal
routers. I use a completely vanilla zebra.conf, and an /etc/quagga/ospfd.conf
config like:
hostname myhost
password mypassword
log syslog
!
router ospf
! Local segments (adjust for your network config and ospf areas)
network 192.168.1.0/24 area 0
! Anycast address redistribution
redistribute connected metric-type 1
distribute-list ANYCAST out connected
!
access-list ANYCAST permit 192.168.255.1/32
That's it. Now (as root) start everything up:
ifup lo:0
for s in dnsmasq zebra ospfd; do
service $s start
chkconfig $s on
done
tail -50f /var/log/messages
And then check on your router that the anycast dns address is getting advertised
and picked up by your router. If you're using cisco, you're probably know how to
do that; if you're using linux and quagga, the useful vtysh commands are:
show ip ospf interface <interface>
show ip ospf neighbor
show ip ospf database
show ip ospf route
show ip route
Wed 20 Aug 2008
Tags: backups, brackup, sysadmin.
Further to my earlier post, I've spent a good chunk
of time implementing brackup over the last few weeks, both at home for my
personal backups, and at $work on some really large trees. There are a few
gotchas along the way, so thought I'd document some of them here.
Active Filesystems
First, as soon as you start trying to brackup trees on any size you find
that brackup aborts if it finds a file has changed between the time it
initially walks the tree and when it comes to back it up. On an active
filesystem this can happen pretty quickly.
This is arguably reasonable behaviour on brackup's part, but it gets
annoying pretty fast. The cleanest solution is to use some kind of
filesystem snapshot to ensure you're backing up a consistent view of your
data and a quiescent filesystem.
I'm using linux and LVM, so I'm using LVM snapshots for this, using
something like:
SIZE=250G
VG=VolGroup00
PART=${1:-export}
mkdir -p /${PART}_snap
lvcreate -L$SIZE --snapshot --permission r -n ${PART}_snap /dev/$VG/$PART && \
mount -o ro /dev/$VG/${PART}_snap /${PART}_snap
which snapshots /dev/VolGroup00/export to /dev/VolGroup00/export_snap, and
mounts the snapshot read-only on /export_snap.
The reverse, post-backup, is similar:
VG=VolGroup00
PART=${1:-export}
umount /${PART}_snap && \
lvremove -f /dev/$VG/${PART}_snap
which unmounts the snapshot and then deletes it.
You can then do your backup using the /${PART}_snap tree instead of your
original ${PART} one.
Brackup Digests
So snapshots works nicely. Next wrinkle is that by default brackup writes its
digest cache file to the root of your source tree, which in this case is
readonly. So you want to tell brackup to put that in the original tree, not
the snapshot, which you do in the your ~/.brackup.conf file e.g.
[SOURCE:home]
path = /export_snap/home
digestdb_file = /exportb/home/.brackup-digest.db
ignore = \.brackup-digest.db$
I've also added an explicit ignore rule for these digest files here. You
don't really need to back these up as they're just caches, and they can get
pretty large. Brackup automatically skips the digestdb_file for you, but it
doesn't skip any others you might have, if for instance you're backing up
the same tree to multiple targets.
Synching Backups Between Targets
Another nice hack you can do with brackup is sync backups on
filesystem-based targets (that is, Target::Filesystem, Target::Ftp, and
Target::Sftp) between systems. For instance, I did my initial home directory
backup of about 10GB onto my laptop, and then carried my laptop into where
my server is located, and then rsync-ed the backup from my laptop to the
server. Much faster than copying 10GB of data over an ADSL line!
Similarly, at $work I'm doing brackups onto a local backup server on the
LAN, and then rsyncing the brackup tree to an offsite server for disaster
recovery purposes.
There are a few gotchas when doing this, though. One is that
Target::Filesystem backups default to using colons in their chunk file names
on Unix-like filesystems (for backwards-compatibility reasons), while
Target::Ftp and Target::Sftp ones don't. The safest thing to do is just to
turn off colons altogether on Filesystem targets:
[TARGET:server_fs_home]
type = Filesystem
path = /export/brackup/nox/home
no_filename_colons = 1
Second, brackup uses a local inventory database to avoid some remote
filesystem checks to improve performance, so that if you replicate a backup
onto another target you also need to make a copy of the inventory database
so that brackup knows which chunks are already on your new target.
The inventory database defaults to $HOME/.brackup-target-TARGETNAME.invdb
(see perldoc Brackup::InventoryDatabase), so something like the following
is usually sufficient:
cp $HOME/.brackup-target-OLDTARGET.invdb $HOME/.brackup-target-NEWTARGET.invdb
Third, if you want to do a restore using a brackup file (the
SOURCE-DATE.brackup output file brackup produces) from a different
target, you typically need to make a copy and then update the header
portion for the target type and host/path details of your new target.
Assuming you do that and your new target has all the same chunks, though,
restores work just fine.
Mon 07 Jul 2008
Tags: backups, brackup, sysadmin.
I've been playing around with Brad Fitzpatrick's
brackup for the last couple of weeks.
It's a backup tool that "slices, dices, encrypts, and sprays across the
net" - notably to Amazon S3,
but also to filesystems (local or networked), FTP servers, or SSH/SFTP
servers.
I'm using it to backup my home directories and all my image and music
files both to a linux server I have available in a data centre (via
SFTP) and to Amazon S3.
brackup's a bit rough around the edges and could do with some better
documentation and some optimisation, but it's pretty useful as it stands.
Here are a few notes and tips from my playing so far, to save others a
bit of time.
Version: as I write the latest version on CPAN is 1.06, but that's
pretty old - you really want to use the
current subversion trunk
instead. Installation is the standard perl module incantation e.g.
# Checkout from svn or whatever
cd brackup
perl Makefile.PL
make
make test
sudo make install
Basic usage is as follows:
# First-time through (on linux, in my case):
cd
mkdir brackup
cd brackup
brackup
Error: Your config file needs tweaking. I put a commented-out template at:
/home/gavin/.brackup.conf
# Edit the vanilla .brackup.conf that was created for you.
# You want to setup at least one SOURCE and one TARGET section initially,
# and probably try something smallish i.e. not your 50GB music collection!
# The Filesystem target is probably the best one to try out first.
# See '`perldoc Brackup::Root`' and '`perldoc Brackup::Target`' for examples
$EDITOR ~/.brackup.conf
# Now run your first backup changing SOURCE and TARGET below to the names
# you used in your .brackup.conf file
brackup -v --from=SOURCE --to=TARGET
# You can also do a dry run to see what brackup's going to do (undocumented)
brackup -v --from=SOURCE --to=TARGET --dry-run
If all goes well you should get some fairly verbose output about all the files
in your SOURCE tree that are being backed up for you, and finally a brackup
output file (typically named SOURCE-DATE.brackup) should be written to your
current directory. You'll need this brackup file to do your restores, but it's
also stored on the target along with your backup, so you can also retrieve it
from there (using brackup-target, below) if your local copy gets lost, or if
you need to restore to somewhere else.
Restores reference that SOURCE-DATE.brackup file you just created:
# Create somewhere to restore to
mkdir -p /tmp/brackup-restore/full
# Restore the full tree you just backed up
brackup-restore -v --from=SOURCE-DATE.brackup --to=/tmp/brackup-restore/full --full
# Or restore just a subset of the tree
brackup-restore -v --from=SOURCE-DATE.brackup --to=/tmp/brackup-restore --just=DIR
brackup-restore -v --from=SOURCE-DATE.brackup --to=/tmp/brackup-restore --just=FILE
You can also use the brackup-target utility to query a target for the
backups it has available, and do various kinds of cleanup:
# List the backups available on the given target
brackup-target TARGET list_backups
# Get the brackup output file for a specific backup (to restore)
brackup-target TARGET get_backup BACKUPFILE
# Delete a brackup file on the target
brackup-target TARGET delete_backup BACKUPFILE
# Prune the target to the most recent N backup files
brackup-target --keep-backups 15 TARGET prune
# Remove backup chunks no longer referenced by any backup file
brackup-target TARGET gc
That should be enough to get you up and running with brackup - I'll
cover some additional tips and tricks in a subsequent post.
Wed 31 Oct 2007
Tags: mysql, nagios, sysadmin.
Here's an interesting one: one of my clients has been seeing mysql
db connections from one of their app servers (and only one) being
periodically locked out, with the following error message reported
when attempting to connect:
Host _hostname_ is blocked because of many connection errors.
Unblock with 'mysqladmin flush-hosts'.
There's no indication in any of the database logs of anything
untoward, or any connection errors at all, in fact. As a workaround,
we've bumped up the max_connect_errors setting on the mysql
instance, and haven't really had time to dig much further.
Till tonight, when I decided to figure out what was going on.
Turns out there's plenty of other people seeing this too, although
MySQL seems to be in "it's not a bug, it's a feature" mode - see
this bug report.
That thread helped clue me in, however. Turns out that mysql counts
any connection to the database, even ones that don't attempt to
make an actual database connection, as a connection error, but they
only log ones that attempt to login. So there's a nice class of
silent errors - and in fact, a nice DOS attack against MySQL - if
you make standard TCP connections to mysql without logging in.
We, being clever and careful, were doing exactly that with
nagios - making a simple TCP connection to
port 3306 - in order to simply and cheaply check that mysql was
listening on that port. Hmmmm.
Easy enough to remedy, of course, once you figure out what's going
on. I even had a nice nagios plugin lying around to let me do more
sophisticated database checks -
check_db_query_rowcount -
so just had to replace the simple check_tcp check with that, and all
is right with the world.
But it's a plain and simple bug, and MySQL need to get it fixed.
Personally I think a simple tcp connection should not count as a
connection error at all without a login attempt (assuming it's not
left half-open etc.). Alternatively, if you do want to count that
as a connection error fine, but at least log some kind of error so
the issue is discoverable and can be handled by someone.
Silent errors are deadly.
