Sunday, 3 February 2013

Work-flow for a Data Centre Relocation

I've relocated a couple of data centres, and I've just started working on another. The last one moved over 600 servers, about half physical and half virtual. We moved over five months, counting from when the first production workload went live in the new data centre. Our team consisted of five PMs working directly with the server, network and storage admins, and application support teams.

[Update: Check out the visual representation of this post here.]

We knew we had a lot of work to do in a short time, and we were working in a diverse and dynamic environment that was changing as we tried to move it. We needed a flexible and efficient way to move the data centre. One thing that really helped was a work-flow for the PMs to work with the various technical and user teams that allowed teams to focus on doing what they needed to do.

Early in the project we collected all the inventory information we could to build up a list of all the servers, whether they were physical or virtual, make and model, O/S, etc., and put it in the Master Device List (MDL). We then did a high-level breakdown into work packets or affinity groups in consultation with the application support folks. These works packets were what was doled out to the individual PMs.

Each PM then began the detailed planning process for the work packet. Starting from a template, the PM began building the relocation plan, which was simply a spreadsheet with a few tabs:
  • One tab was the plan itself, a minute-by-minute description of the tasks that had to be done, and who was responsible for doing them, over the course of the time immediately around the time of the relocation. Many also included the prerequisite tasks in the days preceding the relocation
  • Another tab was the list of servers, and the method by which they would be moved. We had a number of possible move methods, but basically they boiled down to virtual-to-virtual -- copying a virtual machine across the network, lift and shift -- physically moving a server, and leap frog -- copying the image from a physical server across the network to another, identical physical server
  • The third tab was a list of contact information for everyone mentioned in the plan, along with the approvers for the hand-over to production, escalation points, and any other key stakeholders
At this point many PMs also nailed down a tentative relocation date and time for the work packet and put it in the relocation calendar, a shared calendar in Exchange. The relocation calendar was the official source of truth for the timing of relocations. Some PMs preferred to wait until they had more information. My personal preference is to nail down the date early, as you have more choice about when to move.

The PM then got the various admins to gather or confirm the key information for the server build sheet and the server IP list.

The server build sheet contained all the information needed to build the new server in the new data centre. For a virtual machine, this was basically the number and size of mounted storage volumes including the server image itself. This information was key for planning the timing of the relocation, and in the case of VMs with extra attached storage volumes, made sure that everything got moved.

For physical servers the build sheet had everything needed for a VM, plus all the typical physical server information needed by the Facilities team to assign an available rack location and to rack and connect the server in the new data centre.

The server IP list simply listed all the current IPs used by the server, and their purpose. Most of our servers had one connection each to two separate redundant networks for normal data traffic, along with another connection to the backup network, and finally a fourth connection to the out-of-band management network ("lights-out operation" card on the server). Some servers had more, e.g. for connections to a DMZ or ganging two connections to provide more throughput.

The PM iterated through these documents with the admins and support staff until they were ready. One thing that often changed over the course of planning was the list of servers included in the work packet. Detailed analysis often discovered dependencies that brought more servers into the work packet. Or the volume of work proved to be too much to do in the available maintenance window and the work packet had to be split into two. Or the move method turned out to be inappropriate. We encouraged this, as our goal of minimizing or eliminating downtime and risk was paramount.

When the plan was done the Facilities team took the server build sheet and arranged for the physical move and connection of servers. The Network team took the server IP list and used it to assign the new IPs, and prepare the required network configuration and firewall rules.

The network admins put the new IPs into the same server IP list sheet, which was available to everyone, so for example the server admins could assign the new IPs at the time of the relocation.

At the time of the relocation, everyone did their tasks according to the relocation plan, and the PM coordinated everything. For simple single server, single application relocations, the team typically moved and tested the server without intervention from the PM.

Finally, the Backup and Monitoring teams used the server list in the relocation plan to turn backups and monitoring off for the relocated servers at the old data centre, and to turn  backups and monitoring on for the relocated servers at the new data centre.

It wasn't all roses. We had a few challenges.

We set a deadline for the PMs to have the server build sheets and server IP lists completed two weeks before the relocation, to give time for the Facilities team to plan transport and workloads for the server room staff, and for the Network team to check all the firewall rules and ensure that the new configuration files were right. We often missed that deadline, and were saved by great people in the Facilities and Network teams, but not without a lot of stress to them.

There was some duplication of information across the documents, and it could be tedious to update. As an old programmer, I had to stop myself several times from running off and building a little application in Ruby on Rails to manage the process. But we were a relocation project, not a software development project, so we sucked it up and just worked with the tools we had.

In summary, we had a repeatable, efficient work-flow that still allowed us to accommodate the unique aspects of each system we were moving. We needed five key documents:
  • Master device list (MDL), a single spreadsheet for the whole project
  • Relocation calendar, a single shared calendar in Exchange
  • Relocation plan, per work packet
  • Server build sheet, per server, or per work packet with a tab per server
  • Server IP list, a single document for the whole project (which grew as we went)
The PMs were working with various teams that knew how to do, and were very efficient at, certain repeatable tasks:
  • Communicating outages to the user base (Communication Lead)
  • Moving a physical server and connecting it in the new data, or installing a new server as a target for an electronic relocation of a physical server (Facilities team)
  • Moving a virtual machine or a physical machine image, and its associated storage (Server and Storage team)
  • Reconfiguring the network and firewall for the relocated servers, including DNS changes (Network team, although for simple moves the server admin often did the DNS changes)
  • Acceptance testing (Test Lead who organized testing)
  • Changing backups and monitoring (Backup team and Monitoring team)

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