PUBLIC MARKS with tags environment & cluster

smtp-delay is an add-on/plug-in intended for use with qmail. It was written primarily to add banner delays and antipipelining to qmail. These two features are known to be able to block certain types of spam and virus mail sent through non-rfc-compliant SMTP engines. When I looked around for programs to add this functionality to qmail, I found only one such program, and didn't like the way it was done. BTW...I have the same objections to the way its done in sendmail 8.13.x. Since banner delays (the server pausing for some time before issuing an SMTP banner) cause every SMTP connection to take longer, I thought it would be a good idea to somehow exempt "legitimate" mail servers...or at least not subject them to long banner delays. So I decided to tune the banner delay time based on the connecting IP's reverse DNS. IPs with no rDNS get treated the worst (longest banner delay). IPs with rDNS matching a regex intended to detect dynamic/end-user IPs get a moderate delay. All other IPs get a very short banner delay...just long enough to see if they immediately pipeline (send SMTP commands before the banner's been sent). The original intent for smtp-delay was that it should be run before rblsmtpd, and simply set the RBLSMTPD environment variable if applicable, letting rblsmtpd issue the 4xx response. Pretty early on, I realized smtp-delay should be able to run standalone (without dependence on rblsmtpd to do its talking) and issue a 4xx response on its own. Lately, the spam load against our mail cluster has gotten so bad that I've started running smtp-delay after rblsmtpd, based on the idea that there's no point waiting out a long banner delay holding an open socket to an IP we have no intention of accepting mail from anyway. This reduced our concurrency by about 20%.

Scalr is a fully redundant, self-curing and self-scaling hosting environment utilizing Amazon's EC2. It allows you to create server farms through a web-based interface using prebuilt AMI's for load balancers (pound or nginx), app servers (apache, others), databases (mysql master-slave, others), and a generic AMI to build on top of. The health of the farm is continuously monitored and maintained. When the Load Average on a type of node goes above a configurable threshold a new node is inserted into the farm to spread the load and the cluster is reconfigured. When a node crashes a new machine of that type is inserted into the farm to replace it. 4 AMI's are provided for load balancers, mysql databases, application servers, and a generic base image to customize. Scalr allows you to further customize each image, bundle the image and use that for future nodes that are inserted into the farm. You can make changes to one machine and use that for a specific type of node. New machines of this type will be brought online to meet current levels and the old machines are terminated one by one. The project is still very young, but we're hoping that by open sourcing it the AWS development community can turn this into a robust hosting platform and give users an alternative to the current fee based services available.

In this article, I briefly introduce the concepts of Xen virtualization and Linux clustering. From there, I show you how to set up multiple operating systems on a single computer using Xen and how to configure them for use with clustering. I should point out that a cluster implemented in this manner does not provide the computational power of multiple physical computers. It does, however, offer a way to prototype a cluster as well as provide a cost-effective development environment for cluster-based software. Even if you're not interested in clustering, this article gives you hands-on experience using Xen virtualization.

Setting Up An iSCSI Environment On Linux Nowadays, the iSCSI technology is quite popular in the storage world. This article shows an iSCSI demo environment which consists of one Debian Linux host and one Netapp Filer.We try to show the most important features of this protocol. 1. What is iSCSI? It is a network storage protocol above TCP/IP. This protocol encapsulates SCSI data into TCP packets. iSCSI allows us to connect a host to a storage array via a simple Ethernet connection (tape drive). This solution is cheaper than the Fibre Channel SAN (Fibre channel HBAs and switches are expensive). From the host view the user sees the storage array LUNs like a local disks. iSCSI devices should not be confused with the NAS devices (for example NFS). The most important difference is that NFS volumes can be accessed by multiple hosts, but one iSCSI volume can by accessed by one host. It is similar to SCSIi protocol: usually only one host has access to one SCSI disk (the difference is the cluster enviroment). The iSCSI protocol is defined in the RFC3720 document by the IETF (Internet Engineering Task Force).