iTunes could not connect to the iTunes Music Store

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.

iTunes could not connect to the iTunes Music Store

iTunes could not connect to the iTunes Music Store

Getting Started with Amazon EC2

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/ 

How Does DRBD work?

How Does DRBD 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.

UCARP

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.

How Does DRBD work?

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

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/