TweetFollow Us on Twitter

OSX Failover - Part 1

Volume Number: 23 (2007)
Issue Number: 03
Column Tag: Network Administration

OSX Failover - Part 1

A Beginner's Guide

By Ben Greisler

Introduction

OS X Server has the capability to provide IP failover, a high availability feature that allows a secondary backup server to take over for a failed primary server. It is a great feature and can be very handy keeping your services available, but it has its limitations and constraints. We will review the basics of IP failover in this article and then expand on the concept in later issues. This is aimed at getting the beginner up and running with a minimum of hassle.

IP Failover Concepts

There are two major parts to the failover process: The primary server sending out notification that it is up and running and the secondary server monitoring the signal from the primary server. Kind of like, "Can you hear me now?" but without the primary server repeating "Good" after each question. This process is done via two daemons, heartbeatd and failoverd. Both are available on OS X Server, but not on OS X client.

On the primary server, heartbeatd sends out a message every second via port 1694 on both of the network interfaces involved in the process. This is the signal to the other machine in the failover pair that the primary is still alive and well, or at least well enough to keep a heartbeat going.

On the secondary server, failoverd listens for the heartbeat message on port 1694 on both network interfaces. If it stops receiving the heartbeat message it will start the failover process.

Initial configuration of IP failover starts in /etc/hostconfig where you define what role each server will be. We'll get into the specifics in the next section. There is a startup item at /System/Library/StartupItems/IPFailover that checks for configuration specifications and starts either heartbeatd or failoverd located in /usr/sbin as appropriate.

When failoverd on the secondary server realizes that it isn't receiving a heartbeat message, it sets off a series of events based on scripts located in /usr/libexec. The script NotifyFailover grabs the email address of failover recipient from /etc/hostconfig and sends a message to that address. It then utilizes the ProcessFailover script which will make an IP alias on a network interface, allowing the secondary server to take the IP address of the primary server. Both of these scripts are available for examination and are pretty well commented.

Another purpose of the ProcessFailover script is to execute scripts located in the /Library/IPFailover/ folder. This folder does not exist in a standard install of OS X Server and has to be created if needed. Within that folder can be 4 subfolders: PreAcq, PostAcq, PreRel and PostRel. You can utilize these folders to perform certain actions. The names are self-explanatory and define when the content scripts will be used (i.e.: before IP acquisition or after the IP release, etc). This is where the power and flexibility of IP failover resides.

More information can be found in the High Availability Administration document http://images.apple.com/server/pdfs/High_Availability_Admin_v10.4.pdf , but it does have some incorrect information as referenced in this Apple tech article: http://docs.info.apple.com/article.html?artnum=305066

Setting up IP Failover

In this article, we will set up the most basic IP failover configuration to show that it works. In general, IP failover can be done in three easy steps:

1. Set up OSX Server on two machines with appropriate network configurations.

2. Add the appropriate entries to /etc/hostconfig on both machines.

3. Reboot each machine and have a working IP failover pair.

Easy, huh? Ok, now to the steps needed to accommodate the above.

It is best that the two machines in the failover pair be as identical as possible. You wouldn't want the machines to be on different OS versions, or have a secondary server that can't handle the load that the primary server normally handles. It is also tempting to give the secondary server other work to do while it is just sitting there listening to the heartbeat of the primary server, but refrain from that. Its job is to be a backup server, pure and simple.

We need to set up two networks for the IP failover pair to join. One will probably be your existing network that your other machines use to connect to your server. The other network will be a private network that the pair will communicate over. Typically this will be IP over Firewire. You don't have to do it this way, but it does preserve your secondary Ethernet port on machines that have one and allows a private network on machines that don't have a second Ethernet port (i.e.: MacMini).

Let's set up our networking like this:

Primary Server

192.168.254.165 on en0

255.255.255.0 Subnet Mask

192.168.254.1 Gateway

10.0.0.165 on fw0

255.255.0.0 Subnet Mask

Secondary Server

192.168.254.170 on en0

255.255.255.0 Subnet Mask

192.168.254.1 Gateway

10.0.0.170 on fw0

255.255.0.0 Subnet Mask

Make sure that you have good DNS entries for both machines and test them. Do not enter DNS servers or gateway information in the Firewire interface.

Now, let's edit /etc/hostconfig on each server (using your favorite editor via sudo). Add the following lines:

Primary Server

FAILOVER_BCAST_IPS="192.168.254.170 10.0.0.170"

FAILOVER_EMAIL_RECIPIENT=user@domain.com

Secondary Server

FAILOVER_PEER_IP_PAIRS="en0:192.168.254.165"

FAILOVER_PEER_IP="10.0.0.165"

FAILOVER_EMAIL_RECIPIENT=user@domain.com

So, what does all that mean?

FAILOVER_BCAST_IPS="192.168.254.170 10.0.0.170"-This identifies to the primary server the IP addresses of the network interfaces of the secondary server. You can either specify the IP's of the secondary server or use the broadcast addresses for the subnet (i.e.: 192.168.254.255, 10.0.0.255)

FAILOVER_PEER_IP_PAIRS="en0:192.168.254.165"-This identifies the primary interface IP of the primary server. Note the syntax of "en0:" when creating your configuration.

FAILOVER_PEER_IP="10.0.0.165"-This identifies the secondary interface on the primary server. In this case it is the Firewire port (fw0).

FAILOVER_EMAIL_RECIPIENT=user@domain.com-This is the email address of the person who needs to know about failover actions. Make sure that your machine is configured to be able to send mail. You may need to configure SMTP services.

Hook up the servers to the Ethernet network and connect a Firewire cable between the two machines. Check that you can ping each machine on each interface from each machine. Both machines need to be able to see one another. Now restart the primary machine and then the secondary. This is important because if you start the secondary machine before the primary, it won't hear the heartbeat message from the primary and will try to failover immediately.

Ok, now that each server is up and running let's test it out. On a third machine, ping the primary server's public IP address. You should get a good solid return. Now open up Console on each machine and view the System log. Using tail on /var/log/system.log so you can see what is going on with each machine, alternately pull the Firewire cable and then Ethernet cable on the primary machine. You will notice that you stop getting ping responses from the primary server. Wait a few seconds and you should see the pings start to return again. This is the secondary machine reacting to the loss of the heartbeat message from the primary machine and initiating the ProcessFailover script to allow the secondary machine to acquire the IP of the primary machine. You have just gotten IP failover to work!

To failback, I suggest not just plugging the cables back into the primary machine. In a production environment you may have to shutdown the secondary server in a controlled manner, bring the primary back on line and then bring up the secondary. This is inconvenient as it would be great if you could just have everything failback to its original state, but practice has shown that this doesn't happen exactly the way you would want it to in every case.

Conclusion

So, it's great that we can failover from one server to another, but what good does this really do us? In the next article we will start making IP failover do some tricks for us that will be useful. Stay tuned!

References:

http://images.apple.com/server/pdfs/High_Availability_Admin_v10.4.pdf

http://docs.info.apple.com/article.html?artnum=305066

man heartbeatd

man failoverd


Ben has worked Apple based technology integration projects from Maine to Japan while learning all the way. When not collecting frequent flyer miles he spends his favorite time with his wife and 2.5 year old daughter at their home outside of Philadelphia. He can be reached at magikben@mac.com.
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

TotalFinder 1.12.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Features... Read more
Duet 2.3.0.3 - Use your iPad as an exter...
Duet is the first app that allows you to use your iDevice as an extra display for your Mac using the Lightning or 30-pin cable. Note: This app requires a $9.99 iOS companion app. Version 2.3.0.3:... Read more
FileMaker Pro Advanced 18.0.3 - Powerful...
FileMaker Pro Advanced is the tool you use to create a custom app. You also use FileMaker Pro Advanced to access your app on a computer. Start by importing data from a spreadsheet or using a built-in... Read more
OsiriX Lite 10.0.6 - 3D medical image pr...
OsiriX Lite is an image processing software dedicated to DICOM images (".dcm" / ".DCM" extension) produced by medical equipment (MRI, CT, PET, PET-CT, ...) and confocal microscopy (LSM and BioRAD-PIC... Read more
Ableton Live 10.1.5 - Record music using...
Ableton Live lets you create and record music on your Mac. Use digital instruments, pre-recorded sounds, and sampled loops to arrange, produce, and perform your music like never before. Ableton Live... Read more
Burn 2.7.8 - Easily burn data, audio, vi...
Burn... There are a lot of ways to approach burning discs. Burn keeps it simple, but still offers a lot of advanced options. Create data discs with advanced data settings like, file permissions, the... Read more
Malwarebytes 4.0.30.3073 - Adware remova...
Malwarebytes (was AdwareMedic) helps you get your Mac experience back. Malwarebytes scans for and removes code that degrades system performance or attacks your system. Making your Mac once again your... Read more
Acorn 6.5.3 - Bitmap image editor.
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Fantastical 2.5.13 - Create calendar eve...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event... Read more
A Better Finder Rename 11.05 - File, pho...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more

Latest Forum Discussions

See All

Eternal Warfare is a new idle clicker fo...
Idle games are a popular genre on mobile, they might not be to everyone's taste but they're made with such regularity and receive a lot of downloads, so it's hard to argue it's not big business. Eternal Warfare is set to join the sea of idle games... | Read more »
New heroes and balance updates set to ar...
It feels like Hearthstone: Battlegrounds only launched yesterday, and already the auto batter addition to Blizzard's megahit card game is set to receive new heroes and balance updates. [Read more] | Read more »
Pre-register for Hello Kitty AR: Kawaii...
Hello Kitty — the cute cat that launched a multi-billion-pound franchise — has been brought to life… sort of. Sanrio has teamed up with the Bublar Group to create a new mobile game that uses AR tech to turn the real world into Hello Kitty’s... | Read more »
Gorgeous and tranquil puzzler Spring Fal...
One-man indie studio SPARSE//GameDev has now launched its tranquil puzzler, Spring Falls. It's described as "a peaceful puzzle game about water, erosion, and watching things grow". [Read more] | Read more »
Black Desert Mobile gets an official rel...
Pearl Abyss has just announced that its highly-anticipated MMO, Black Desert Mobile, will launch globally for iOS and Android on December 11th. [Read more] | Read more »
Another Eden receives new a episode, cha...
Another Eden, WFS' popular RPG, has received another update that brings new story content to the game alongside a few new heroes to discover. [Read more] | Read more »
Overdox guide - Tips and tricks for begi...
Overdox is a clever battle royale that changes things up by adding MOBA mechanics and melee combat to the mix. This new hybrid game can be quite a bit to take in at first, so we’ve put together a list of tips to help you get a leg up on the... | Read more »
Roterra Extreme - Great Escape is a pers...
Roterra Extreme – Great Escape has been described by developers Dig-It Games as a mini-sequel to their acclaimed title Roterra: Flip the Fairytale. It continues that game's tradition of messing with which way is up, tasking you with solving... | Read more »
Hearthstone: Battlegrounds open beta lau...
Remember earlier this year when auto battlers were the latest hotness? We had Auto Chess, DOTA Underlords, Chess Rush, and more all gunning for our attention. They all had their own reasons to play, but, at least from where I'm standing, most... | Read more »
The House of Da Vinci 2 gets a new gamep...
The House of Da Vinci launched all the way back in 2017. Now, developer Blue Brain Games is gearing up to deliver a second dose of The Room-inspired puzzling. Some fresh details have now emerged, alongside the game's first official trailer. [Read... | Read more »

Price Scanner via MacPrices.net

B&H offers $100 discounts on 4-Core and 6...
B&H Photo has new 4-Core and 6-Core Mac minis in stock and on sale today for $100 off Apple’s MSRP. Prices start at $699. Overnight shipping is free to many addresses in the US: – 3.6GHz Quad-... Read more
Save $200 today on a 2019 13″ MacBook Air wit...
Apple has a full line of Certified Refurbished 2019 13″ MacBook Airs available starting at only $929 and up to $200 off the cost of new Airs. Each MacBook features a new outer case, comes with a... Read more
New Verizon Pre-Black Friday 2019 deal: Buy o...
Buy one new Apple iPhone 11 model or 2018 iPhone XS model at Verizon and get a second one for free. One new line of service required. Offer is valid from November 21, 2019 to November 27, 2019. Here... Read more
AirPods with Wireless Charging Case on sale t...
Abt Electronics has 2019 AirPods with the Wireless Charging Case on sale today for $163 shipped. Their price is $36 off Apple’s MSRP, and it’s currently the cheapest price for these AirPods from any... Read more
Apple continues to offer 2017 13″ Dual-Core n...
Apple has Certified Refurbished 2017 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros still available starting at $1019. An standard Apple one-year warranty is included with each model, outer cases... Read more
Save up to $120 on the new 16″ MacBook Pro at...
Apple’s resellers are starting to receive stock of new 16″ MacBook Pros, and the first set of sales & deals are now available: (1) Amazon 16″ MacBook Pros start on sale for $100-$116 off Apple’s... Read more
Apple Watch Series 3 models on sale at Amazon...
Amazon has Apple Watch Series 3 GPS models on sale for $30 off MSRP, starting at only $169. There prices are the lowest we’ve ever seen for these models from any Apple reseller. Choose Amazon as the... Read more
The ‘Mac Potpourri’ Mailbag: Edition #1- Info...
COMMENTARY: 11.20.19- Welcome to the inaugural edition of the “Mac Potpourri” Mailbag where we take a look at correspondence received from readers of this column from all over the world who write in... Read more
13″ 2.4GHz MacBook Pros available for up to $...
Apple has a full line of Certified Refurbished 2019 13″ 2.4GHz 4-Core Touch Bar MacBook Pros available starting at $1529 and up to $300 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
New at T-Mobile: Switch to T-Mobile, and get...
T-Mobile is offering a free 64GB iPhone 8 for new customers who switch to T-Mobile and open a new line of service. Eligible trade-in required, and discount applied over a 24 month period. The fine... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**747303BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 001413-Cypress-Store **Job Description:** **What Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**743221BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000230-Greenwood-Store **Job Description:** At Best Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**747338BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000254-Superstition Springs-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**745516BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001101-Manhattan-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**746655BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 002518-Atlantic Center-Store **Job Description:** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.