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'''Question''': I don't remember deciding on using Cyrus IMAP. We currently use Courier, and I know that the formats the two use are incompatible. I also believe that Cyrus has more overhead needed to get it going, but that it scales better, especially to cases where most e-mail accounts aren't associated with UNIX usernames. Is that why you chose it? The other two daemons you listed are what we already ready. --AdamChlipala

1. Details about the next Hcoop Architecture

This page is intended to facilitate discussion of details relating to our next server architecture. Currently, the first draft of this page, written on Sat Mar 25 10:18:12 EST 2006 by JustinLeitgeb, is based upon discussions from the hcoop mailing list. Please feel free to contribute or change anything here!

1.1. Hcoop Future Network Overview

The architecture for the next hcoop.net network involves three physical servers:

  • A fileserver, running AFS which is accessible via ssh only for administrative purposes
  • A public login and http server, accessible by all members. User files are stored on the fileserver mentioned above. This will host all user pages, including dynamic content.
  • A server for hcoop needs that most users won't need direct shell access to. This will run Cyrus IMAP, exim, and Apache primarily for hcoop administrative purposes.

Question: I don't remember deciding on using Cyrus IMAP. We currently use Courier, and I know that the formats the two use are incompatible. I also believe that Cyrus has more overhead needed to get it going, but that it scales better, especially to cases where most e-mail accounts aren't associated with UNIX usernames. Is that why you chose it? The other two daemons you listed are what we already ready. --AdamChlipala

Additionally, we will need certain networking equipment:

  • A gigabit switch that will be the initial backbone of the hcoop LAN.
  • Perhaps (still not finalized in plans) a hardware firewall for the hcoop LAN. Ideas on this from members?

We should also remember that all of our servers will most likely have at least two NIC's. How can we utilize these best? Some sites have one NIC doing backups or logging, and another handling requests from the Internet. Perhaps we could segment our traffic to two local area networks, one for services to the Internet and another for local file access (i.e., traffic between the two "public" servers and the file server).

1.2. Hcoop Future Network Diagrams

The following are a preliminary version of a network plan that JustinLeitgeb created on March 25, 2006, after discussions on the hcoop.net mailing list. Included in the design is a hardware firewall, which was not finalized in previous discussions. Let's collect thoughts and alternate plans here as we work towards solidifying plans.

  • [attachment:network_diagram_20060325.dia Network planning diagram in "dia" format for editing]
  • [attachment:network_diagram_20060325.png Network planning diagram in PNG format for easier viewing]

1.3. Server Hardware

This may be a moot point as we are looking for a shop that can give us hardware support, and this may require that we buy their supported machines. However, it seems that many colocation providers will try to push us into a deal where their support consists in a "remote hands" plan where they will fix any reasonably standard hardware that we send to them for an hourly rate. If that is the case, our discussions on possible server hardware on the list may still be valid. Generally, we have decided that what we need in terms of hardware is more or less as follows:

  • Two web servers with at least 1GB of RAM each. Redundancy should include a RAID 1 configuration with two 73 GB drives, and dual power supplies.
  • One file server with more storage space and room to grow. It doesn't need to be exceptionally fast because of AFS's caching mechanisms. Perhaps a small RAID 5 configuration of 3 x 500 GB SATA devices would be a good place to start. It should certainly be hardware - based RAID so that main CPU power is not needed for read and write operations. JustinLeitgeb suggested a [http://www.3ware.com/products/serial_ata2-9000.asp 3Ware Escalade Controller] in this machine.

The list also discussed hardware vendors. If this isn't a moot point based on our decision of a colo provider with specific needs, the following list of possibilities may still be relevant:

1.4. Networking Hardware

Here we should talk about the specific networking equipment that we need. Ideas on vendors or models for the gigabit switch? Thoughts on if we should start with a hardware firewall device? Also it was mentioned that we should invest in a serial console for remote access when a machine goes down. Thoughts on this?

1.5. Backup Configuration

All are in agreement that we need a robust backup plan in our new architecture. It seems that it will include the continued use of [ http://www.rsnapshot.org rsnapshot], and that this utility will save even the front-end server data to the fileserver with RAID 5. Additionally, we should have data stored off-site in a manner that allows us to recover, even in the event that we are "rooted". We are looking for backup capabilities in colocation providers. Another option could be to have rsync-style backups to some administrators connection over the Internet, but this might not be tenable given the amount of data, the need for quick restores, etc. Let's continue to edit this section!

1.6. Scaling Out

The next configuration should be reasonably scaleable, as we are expecting to grow rapidly in size. How should we scale our systems? Some ideas follow:

  • Make sure our software is able to publish to a web cluster. Eventually, we may have a dedicated "development" web node with a testing apache configuration. Once they are satisfied with their changes, they could push out these changes to a cluster. This could just mean putting them in a special location on the fileserver that is pulled from by a set of web nodes. Think about how to do load balancing on this cluster. F5 Networks has a device that will load-balance, but perhaps a linux solution would be more affordable.
  • Precisely how do we scale our fileserver? Does AFS have a mechanism where new fileservers can be added to the available space? Is RAID 5 the best solution, or should be start with something like RAID 10 for better IO throughput? Will AFS caching to the front-end web nodes be sufficient to mitigate the latency that will be introduced by a relatively slow RAID 5 configuration?
  • Database clustering possibilities: Many of our sites seem to depend on MySQL. In the future, something like MySQL clustering may help us by having a tuned database cluster to be shared by a lot of dynamic web sites. This could then be put behind a VIP (Virtual IP).

1.7. Page version history

Initial page created Sat Mar 25 11:52:03 EST 2006 JustinLeitgeb.

ColocationPlans is the main page for items related to the new architecture. ColocationPlansServiceProviders provides information about the service providers we are currently looking at.

SystemArchitecturePlans (last edited 2012-12-14 17:03:35 by ClintonEbadi)