Kenjun TechBits

On my MacBook I got this message…

iTunes could not connect to the iTunes Music Store

Tried different versions of iTunes from 7.4.2 to 7.5 and 7.6 but no luck.
I then tried running iTunes on WindowsXP on the same MacBook via Parallels which connected. I installed Little Snitch to see what was happening to the network connections and found out iTunes wasn’t even attempting to connect.

The problem turned out to be a proxy configuration file (PAC) which had been setup in System Preferences | Network | Airport | Advanced | Proxies

As soon as I removed it, the problem disappeared.

EC2 is all about the “elastic compute cloud.” In layman’s terms, it’s a server. In slightly less layman’s terms, EC2 lets you easily run and manage many instances (like servers) and given the proper software and configurations, have a scalable platform for your web application, outsource resource-intensive tasks to EC2 or for whatever you would use a server farm.

http://paulstamatiou.com/2008/04/05/how-to-getting-started-with-amazon-ec2

AWS Simple Monthly Calculator

http://calculator.s3.amazonaws.com/calc5.html 

and an alternative to EC2 using a VPS system such as Slicehost

http://www.slicehost.com/ 

What is UCARP

UCARP allows a couple of hosts to share common virtual IP addresses in order to provide automatic failover. It is a portable userland implementation of the secure and patent-free Common Address Redundancy Protocol (CARP, OpenBSD’s alternative to the patents-bloated VRRP).

Strong points of the CARP protocol are: very low overhead, cryptographically signed messages, interoperability between different operating systems and no need for any dedicated extra network link between redundant hosts.

WhatsUp is software that does network management

http://www.whatsupgold.com/products/index.asp

How does it work ?

Each device (DRBD provides more than one of these devices) has a state, which can be ‘primary’ or ’secondary’. On the node with the primary device the application is supposed to run and to access the device (/dev/drbdX). Every write is sent to the local ‘lower level block device’ and to the node with the device in ’secondary’ state. The secondary device simply writes the data to its lower level block device. Reads are always carried out locally.

If the primary node fails, heartbeat is switching the secondary device into primary state and starts the application there. (If you are using it with a non-journaling FS this involves running fsck)

If the failed node comes up again, it is a new secondary node and has to synchronise its content to the primary. This, of course, will happen whithout interruption of service in the background.

And, of course, we only will resynchronize those parts of the device that actually have been changed. DRBD has always done intelligent resynchronization when possible. Starting with the DBRD-0.7 series, you can define an “active set” of a certain size. This makes it possible to have a total resync time of 1–3 min, regardless of device size (currently up to 4TB), even after a hard crash of an active node.

What is DRBD

DRBD is a block device which is designed to build high availability clusters. This is done by mirroring a whole block device via (a dedicated) network. You could see it as a network raid-1.

DRBD is copyright by Philipp Reisner, Lars Ellenberg and LinBit.

What is the scope of drbd, what else do I need to build a HA cluster?

DRBD takes over the data, writes it to the local disk and sends it to the other host. On the other host, it takes it to the disk there.

The other components needed are a cluster membership service, which is supposed to be heartbeat, and some kind of application that works on top of a block device.

Examples:

A filesystem & fsck.

A journaling FS.

A database with recovery capabilities.

http://www.drbd.org/

Several solutions see to do the job.

These are:

• Singular
• dupeGuru
• MrClean
• FileBuddy9

Review:

I created a 2.7 GB directory of various duplicated files and ran them against each other.

Fastest: Singular, closely followed by dupeGuru. MrClean and FileBuddy trailed a long way behind.

Easiest to use: Singular starts off with a window asking you to drag your files into it. Super-simple. dupeGuru has more options on the initial screen which can be cumbersome. For example, you have to select which directories you wish to scan. However, the additional options allow you to add two different directories and also sort by size - very useful. MrClean and FileBuddy again have a rather complex initial setup.

Cons: FileBuddy obviously suffers from being an all-in-one application.

In conclusion, for a single directory, Singular is by far the easiest. However, if you wish to sort by size and/or check for duplicates on multiple directories then with dupeGuru wins out. One other consideration is that Singular has occasionally crashed with big directories whereas dupeGuru completed a 62GB directory scan comfortably.

This may be a DNS problem in Firefox.

Check out these articles….

Firefox: “Looking up…” Takes Too Long [RESOLVED {for sure this time}] 

and the MozillaZine article:

Network.dns.ipv4OnlyDomains

From MozillaZine:

IPv6 is a new version of the Internet Protocol that will be used in the future instead of IPv4. Not all web servers correctly support IPv6, and this can lead to connection failures and delays in loading websites. This preference controls which servers to use IPv4 on even if IPv6 is enabled

Possible values and their effects

A comma-seperated list of domains to connect with IPv4 instead of IPv6. Default value is .doubleclick.net; in trunk builds this has been changed to an empty string.

Caveats

• network.dns.disableIPv6 must be set to false for this preference to take effect

Recommended settings

The default setting for this preference does not mean that Mozilla will ever contact doubleclick.net (an internet ad company) if it is not requested, it just specifies which IP version to use if it is requested. The .doubleclick.net address was originally added because their DNS server was broken and caused delays in page loads; this has since been fixed. If you wish, you may delete this preference with no ill effects.

sudo apachectl restart

or if you’re not sure that it’s working, do it in stages:

sudo apachectl stop

and then

sudo apachectl start

http://snippets.dzone.com/posts/show/1878

A super simple shell script which does all the boring configuration for setting up a virtual host on MacOSX. Works in Leopard too!

 http://patrickgibson.com/utilities/virtualhost/