I spent an interesting few days last week at the Velocity 2010 conference in Santa Clara. The focus of the conference was on performance and application operations for large-scale web apps. Here are my take-aways:
Fundamentally a problem of scale-out, of handling online communities of millions of users and the massive amounts of information that they want at hand. As Theo Schlossnagle pointed out in an excellent workshop on Scalable Internet Architectures (or you can read the book…), the players in this space approach performance problems with similar technologies (LAMP or something similar like Ruby on Rails as the principal stack, and commodity servers) and architectural strategies:
1. Data partitioning – sharding datasets across commodity servers, required because MySQL does not scale vertically. Theo’s advice on sharding: “Avoid sharding as long as possible, it is painful. If you have to shard, follow these steps. Step 1: Shard your data. Step 2: Shoot yourself”. Consider duplicating data if you need the same information available in different partitioning schemes.
2. Non-ACID key-value data stores and NOSQL distributed data managers like Cassandra, MongoDB, Voldemort, Redis or CouchDB for handing high volumes of write-intensive data. Fast and simple, but these technologies are still immature, they are not hardened or reliable, and they lack the kinds of management capabilities and tools that Oracle DBAs have been accustomed to for years.
3. Strategies for effective caching of high-volume data, basically ways of extending and optimizing the use of memcached, and different schemes for effective cache consistency and cache coherency.
Some other advice from Theo: Planning for more than a 10-fold increase in workload is a waste of time – you won’t understand the type of problems that you are going to face until you get closer. On architecture and design: don’t simplify simple problems.
Coming from a financial trading background, I was surprised to see that the argument still needed to be made that performance was an important business factor: that speed could improve business opportunities. Seems obvious.
According to one of the keynote speakers, Urz Holzle at Google, the average time for a page to load is 4.9 seconds, while the goal should be around 100 ms – the time that it takes a reader to turn a page in a book. Google presented some interesting research work that they are leading to improve the front-end response time of the web experience, including proposals to improve DNS and TCP, work done in Chrome to improve browser performance, and advanced performance profiling tools made available to the community.
Operations and DevOps
Provisioning and deployment (a real management problem when you need to deploy to thousands or tens of thousands of servers); change management and the rate of change; version control and other disciplines; instrumentation and logging; metrics and more metrics; and failure handling and incident management.
Log and measure as much as you can about the application and infrastructure – establish baselines, understand Normal, understand how the system looks when it is working correctly and is healthy.
Configuration management and deployment. Advice from Theo: version control everything – not just code and application configuration, and server configs, but also the configs for firewalls and load balancers and switches/routers and the database schemas and…
Several companies were using Chef or Puppet for managing configuration changes. Facebook and Twitter were both using BitTorrent to stream code updates across thousands of servers.
Change management. The consensus is that ITIL is very uncool – it is all about being slow and bureaucratic. This is a shame – I think that everyone in an operations role could learn from the basics of ITIL and Visible Ops, the disciplines and frameworks.
The emphasis was on how to effect rapid change, how to get feedback as quickly as possible, time to market, continuous prototyping, A/B split testing to understand customer needs, the need to make decisions quickly and see results quickly. At the same time, different speakers stressed the need for discipline and responsibility and accountability: that the person who is responsible for making a change should make sure it gets deployed properly, and that it works.
Continuous Deployment came up several times, although “Continuous” means different things to different people. For Facebook this means pushing out small changes and patches every day and features once per week.
You can’t make changes without taking on the risk of failure. This was especially clear to an audience where so many people had experience in startups.
Lenny Rachitsky’s session, The Upside of Downtime, covered the need for transparency in the event of failure, and showed how being transparent and honest in the event of a failure can help build customer confidence. His blog, Transparent Uptime includes an interesting collection of Public Health Dashboards for web communities.
To succeed you need to learn from failures of course – use postmortems and Root Cause Analysis to understand what happened and implement changes so that you don’t keep making the same mistakes. Another quote from Theo: “Good judgment comes from experience. Experience comes from bad judgment. Allow people to make mistakes – but limit the liability. Measure the poise and integrity with which someone deals with the problem and its remediation.”
So failure can scorch you, make you afraid, and this fear can affect your decision making, slow you down, stop you from taking on necessary and manageable risks. You need to know how much risk you can take on, whether you are going too slow or too fast, and how to move forward.
John Allspaw at Etsy, one of the rock stars of the devops community, made a clear and compelling (and entertaining) case for meta-metrics, data to provide confidence in your operational decisions: “How do we get confidence in [what we are doing]? We make f*&^ing graphs!”
First track all changes: who made the change, when, what type, and how much was changed. Track all incidents: severity, time started, time to detect, time to recover/resolve, and the cause (determined by RCA). Then correlate changes with incidents: by type, size, frequency. With this you can answer questions like: What type of incidents have high Time to Recover? What types of changes have high / low success rates?
Unfortunately the video and slide deck for this presentation are not available on the Velocity site yet.
There was some macho bullshit from one of the speakers about “failing forward” – that essentially rolling back was for cowards. I think this statement was made tongue-in-cheek and I hope that it was taken as such by the audience.
I also followed up some more on Cloud Computing. Sure, the Cloud gives you cheap access to massive resources but the consensus at the conference was that it is still not reliable and it is definitely not safe, and it doesn’t look like it will get that way soon. Any data that you need to be safe or confidential needs to be kept out of the Cloud or at minimum encrypted and signed with the keys and other secrets stored out of the Cloud, following a public/private data architecture.
The conference was fun and thought-provoking, and I met a lot of smart and thoughtful people. The crowd was mostly young and attention-deficit: iphones, ipads, notebooks and laptops in constant use throughout the sessions.
Maybe it was the California sunshine, but the atmosphere was more open, more sharing, and less proprietary than I am used to – there was a refreshing amount of transparency into the technology and operations at many of the companies. The vendor representation was small and low key, but recruitment was blatant and pervasive: everyone was hunting for talent.
I am an uptight enterprise guy. It would be fun to work on large-scale consumer problems, with more freedom to make changes. I regret missing the followon DevOps Days event last Friday but I had to get home. And finally, I am looking forward to getting my copy of the new WebOps book
which was premiered at the conference, and to next years Velocity conference.