Monday, October 24, 2011

Rolling Forward and other Deployment Myths

There is more and more writing on Devops lately, which is good and bad. There still remains a small core of thoughtful people that are worth listening to and learning from. There’s more and more marketing from vendors and consultants jumping on the Devops bandwagon. There’s some na├»ve silliness (“Hire wicked smart people and give them all access to root.”) which can probably be safely ignored. And then there’s stuff that is half-right and half-wrong, too dangerous to be ignored. Like this recent post on Rollbacks and Other Deployment Myths, in which John Vincent lists 5 “myths” about system deployment, which I want to take some time to respond to here.

Change is change?

The author tries to make the point that “Change is neither good or bad. It’s just change.” Therefore we do not need to be afraid of making changes.

I don’t agree. This attitude to change ignores the fact that once a system is up and running and customers are relying on it to conduct their business, whatever change you are making to the system is almost never as important as making sure that the system keeps running properly. Unfortunately, changes often lead to problems. We know from Visible Ops that based on studies of hundreds of companies, 80% of operational failures are caused by mistakes made during changes. This is where heavyweight process control frameworks like ITIL and COBIT, and detective change control tools like Tripwire came from. To help companies get control over IT change, because people had to find some way to stop shit from breaking.

Yes, I get the point that in IT we tend to over-compensate, and I agree that calling in the Release Police and trying to put up a wall around all changes isn’t sustainable. People don’t have to work this way. But trivializing change, pretending that changes don't lead to problems, is dangerous.

Deploys are not risky?

You can be smart and careful and break changes down into small steps and try to automate code pushes and configuration changes, and plan ahead and stage and review and test all your changes, and after all of this you can still mess up the deploy. Even if you make frequent small changes and simplify the work and practice it a lot.

For systems like Facebook and online games and a small number of other cases, maybe deployment really is a non-issue. I don’t care if Facebook deploys in the middle of the day – I can usually tell when they are doing a “zero downtime” deploy (or maybe they are “transparently” recovering from a failure) because data disappears temporarily or shows up in the wrong order, functions aren’t accessible for a while, forms don’t resolve properly, and other weird shit happens, and then things come back later or they don’t. As a customer, do I care? No. It’s an inconvenience, and it’s occasionally unsettling ("WTF just happened?"), but I get used to it and so do millions of others. That’s because most of us don’t use Facebook or systems like this for anything important.

For business-critical systems handling thousands of transactions a second that are tied into hundreds of other company’s systems (the world that I work in) this doesn’t cut it. Maybe I spend too much time at this extreme, where even small problems with compatibility that only affect a small number of customers, or slight and temporary performance slow downs, are a big deal. But most people I work with and talk to in software development and maintenance and system operations agree that deployment is a big deal and needs to be done with care and attention, no matter how simple and small the changes are and no matter how clean and simple and automated the deployment process is.

Rollbacks are a myth?

Vincent wants us to “understand that it’s typically more risky to rollback than rolling forward. Always be rolling forward.”

Not even the Continuous Deployment advocates (who are often some of the most radical – and I think some of the most irresponsible – voices in the Devops community) agree with this – they still roll back if they find problems with changes.

“Rollbacks are a myth” is an echo of the “real men fail forward” crap I heard at Velocity last year and it is where I draw the line. It's one thing to state an extreme position for argument's sake or put up a straw man – but this is just plain wrong.

If you're going to deploy, you have to anticipate roll back and think about it when you make changes and you have to test rolling back to make sure that it works. All of this is hard. But without a working roll back you have no choice other than to fail forward (whatever this means, because nobody who talks about it actually explains how to do it), and this is putting your customers and their business at unnecessary risk. It’s not another valid way of thinking. It’s irresponsible.

James Hamilton wrote an excellent paper on Designing and Delivering Internet-Scale Services when he was at Microsoft (now he’s a an executive and Distinguished Engineer at Amazon). Hamilton’s paper remains one of the smartest things that anyone has written about how to deal with deployment and operational problems at scale. Everyone who designs, builds, maintains or operates an online system should read it. His position on roll back is simple and obvious and right:
Reverting to the previous version is a rip cord that should always be available on any deployment.
Everything fails. Embrace failure.

I agree that everything can and will fail some day, that we can’t pretend that we can prevent failures in any system. But I don’t agree with embracing failure, at least in business-critical enterprise systems, where recovering from a failure means lost business and requires unraveling chains of transactions between different upstream and downstream systems and different companies, messing up other companies' businesses as well as your own and dealing the follow-on compliance problems. Failures in these kinds of systems, and a lot of other systems, are ugly and serious, and they should be treated seriously.

We do whatever we can to make sure that failures are controlled and isolated, and we make sure that we can recover quickly if something goes wrong (which includes being able to roll back!). But we also do everything that we can to prevent failures. Embracing failure is fine for online consumer web site startups – let’s leave it to them.

SLAs

I wanted to respond to the points about SLAs, but it’s not clear to me what the author was trying to say. SLAs are not about servers. Umm, yes that’s right of course...

SLAs are important to set business expectations with your customers (the people who are using the system) and with your partners and suppliers. So that your partners and suppliers know what you need from them and what you are paying them for, and so that you know if you can depend on them when you have to. So that your customers know what they are paying you for. And SLAs (not just high-level uptime SLAs, but SLAs for Recovery Time and Recovery Point goals and incident response and escalation) are important so that your team understands the constraints that they need to work under, what trade-offs to make in design and implementation and in operations.

Under-compensating is worse than Over-compensating

I spent more time than I thought I would responding to this post, because some of what the author says is right – especially in the second part of his post, Deploy All the Things where he provides some good practical advice on how to reduce risk in deployment. He’s right that Operations main purpose isn’t to stop change – it can’t be. We have to be able to keep changing, and developers and operations have to work together to do this in safe and efficient ways. But trivializing the problems and risks of change and over-simplifying how to deal with these risks and how to deal with failures, isn’t the way to do this. There has to be a middle way between the ITIL and COBIT world of controls and paper and process, and cool Web startups failing forward, a way that can really work for the rest of us.

Wednesday, October 12, 2011

You can’t be Agile in Maintenance?

I’ve been going over a couple of posts by Steve Kilner that question whether Agile methods can be used effectively in software maintenance. It’s a surprising question really. There are a lot of maintenance teams who have had success following Agile methods like Scrum and Extreme Programming (XP) for some time now. We’ve been doing it for almost 5 years, enhancing and maintaining and supporting enterprise systems, and I know that it works.

Agile development naturally leads into maintenance – the goal of incremental Agile development is to get working software out to customers as soon as possible, and get customers using it. At some point, when customers are relying on the software to get real business done and need support and help to keep the system running, teams cross from development over to maintenance. But there’s no reason for Agile development teams to fundamentally change the way that they work when this happens.

It is harder to introduce Agile practices into a legacy maintenance team – there are a lot of technical requirements and some cultural changes that need to be made. But most maintenance teams have little to lose and lots to gain from borrowing from what Agile development teams are doing. Agile methods are designed to help small teams deal with a lot of change and uncertainty, and to deliver software quickly – all things that are at least as important in maintenance as they are in development. Technical practices in Extreme Programming especially help ensure that the code is always working – which is even more important in maintenance than it is in development, because the code has to work the first time in production.

Agile methods have to be adapted to maintenance, but most teams have found it necessary to adapt these methods to fit their situations anyways. Let’s look at what works and what has to be changed to make Agile methods like Scrum and XP work in maintenance.

What works well and what doesn’t

Planning Game

Managing maintenance isn’t the same as managing a development project – even an Agile development project. Although Agile development teams expect to deal with ambiguity and constant change, maintenance teams need to be even more flexible and responsive, to manage conflicts and unpredictable resourcing problems. Work has to be continuously reviewed and prioritized as it comes in – the customer can’t wait for 2 weeks for you to look at a production bug. The team needs a fast path for urgent changes and especially for hot fixes.

You have to be prepared for support demands and interruptions. Structure the team so that some people can take care of second-level support, firefighting and emergency bug fixing and the rest of the team can keep moving forward and get something done. Build slack into schedules to allow for last-minute changes and support escalation.

You will also have to be more careful in planning out maintenance work, to take into account technical and operational dependencies and constraints and risks. You’re working in the real world now, not the virtual reality of a project.

Standups

Standups play an important role in Agile projects to help teams come up to speed and bond. But most maintenance teams work fine without standups – since a lot of maintenance work can be done by one person working on their own, team members don’t need to listen to each other each morning talking about what they did yesterday and what they’re going to do – unless the team is working together on major changes. If someone has a question or runs into a problem, they can ask for help without waiting until the next day.

Small releases

Most changes and fixes that maintenance teams need to make are small, and there is almost always pressure from the business to get the code out as soon as it is ready, so an Agile approach with small and frequent releases makes a lot of sense. If the time boxes are short enough, the customer is less likely to interrupt and re-prioritize work in progress – most businesses can wait a few days or a couple of weeks to get something changed.

Time boxing gives teams a way to control and structure their work, an opportunity to batch up related work to reduce development and testing costs, and natural opportunities to add in security controls and reviews and other gates. It also makes maintenance work more like a project, giving the team a chance to set goals and to see something get done. But time boxing comes with overhead – the planning and setup at the start, then deployment and reviews at the end – all of which adds up over time. Maintenance teams need to be ruthless with ceremonies and meetings, pare them down, keep only what’s necessary and what works.

It’s even more important in maintenance than in development to remember that the goal is to deliver working code at the end of each time box. If some code is not working, or you’re not sure if it is working, then extend the deadline, back some of the changes out, or pull the plug on this release and start over. Don’t risk a production failure in order to hit an arbitrary deadline. If the team is having problems fitting work into time boxes, then stop and figure out what you’re doing wrong – the team is trying to do too much too fast, or the code is too unstable, or people don’t understand the code enough – and fix it and move on.

Reviews and Retrospectives

Retrospectives are important in maintenance to keep the team moving forward, to find better ways of working, and to solve problems. But like many practices, regular reviews reach a point of diminishing returns over time – people end up going through the motions. Once the team is setup, reviews don’t need to be done in each iteration unless the team runs into problems.

Schedule reviews when you or the team need them. Collect data on how the team is working, on cycle time and bug report/fix ratios, correlate problems in production with changes, and get the team together to review if the numbers move off track. If the team runs into a serious problem like a major production failure, then get to the bottom of it through Root Cause Analysis.

Sustainable pace / 40-hour week

It’s not always possible to work a 40-hour week in maintenance. There are times when the team will be pushed to make urgent changes, spend late nights firefighting, releasing after hours and testing on weekends. But if this happens too often or goes on too long the team will burn out. It’s critical to establish a sustainable pace over the long term, to treat people fairly and give them a chance to do a good job.

Pairing

Pairing is hard to do in small teams where people are working on many different things. Pairing does make sense in some cases – people naturally pair-up when trying to debug a nasty problem or walking through a complicated change – but it’s not necessary to force it on people, and there are good reasons not to.

Some teams (like mine) rely more on code reviews instead of pairing, or try to get developers to pair when first looking at a problem or change, and at the end again to review the code and tests. The important thing is to ensure that changes get looked at by at least one other person if possible, however this gets done.

Collective Code Ownership

Because maintenance teams are usually small and have to deal with a lot of different kinds of work, sooner or later different people will end up working on different parts of the code. It’s necessary, and it’s a good thing because people get a chance to learn more about the system and work with different technologies and on different problems.

But there’s still a place for specialists in maintenance. You want the people who know the code the best to make emergency fixes or high-risk changes – or at least have them review the changes – because it has to work the first time. And sometimes you have no choice – sometimes there is only one person who understands a framework or language or technical problem well enough to get something done.

Coding Guidelines – follow the rules

Getting the team to follow coding guidelines is important in maintenance to help ensure the consistency and integrity of the code base over time – and to help ensure software security. Of course teams may have to compromise on coding standards and style conventions, depending on what they have inherited in the code base; and teams that maintain multiple systems will have to follow different guidelines for each system.

Metaphor

In XP, teams are supposed to share a Metaphor: a simple high-level expression of the system architecture (the system is a production line, or a bill of materials) and common names and patterns that can be used to describe the system. It’s a fuzzy concept at best, a weak substitute for more detailed architecture or design, and it’s not of much practical value in maintenance. Maintenance teams have to work with the architecture and patterns that are already in place in the system.

What is important is making sure that the team has a common understanding of these patterns and the basic architecture so that the integrity isn’t lost – if it hasn’t been lost already. Getting the team together and reviewing the architecture, or reverse-engineering it, making sure that they all agree on it and documenting it in a simple way is important especially when taking over maintenance of a new system and when you are planning major changes.

Simple Design

Agile development teams start with simple designs and try to keep them simple. Maintenance teams have to work with whatever design and architecture that they inherit, which can be overwhelmingly complex, especially in bigger and older systems. But the driving principle should still be to design changes and new features as simple as the existing system lets you – and to simplify the system’s design further whenever you can.

Especially when making small changes, simple, just-enough design is good – it means less documentation and less time and less cost. But maintenance teams need to be more risk adverse than development teams – even small mistakes can break compatibility or cause a run-time failure or open a security hole. This means that maintainers can’t be as iterative and free to take chances, and they need to spend more time upfront doing analysis, understanding the existing design and working through dependencies, as well as reviewing and testing their changes for regressions afterwards.

Refactoring

Refactoring takes on a lot of importance in maintenance. Every time a developer makes a change or fix they should consider how much refactoring work they should do and can do to make the code and design clearer and simpler, and to pay off technical debt. What and how much to refactor depends on what kind of work they are doing (making a well-thought-out isolated change, or doing shotgun surgery, or pushing out an emergency hot fix) and the time and risks involved, how well they understand the code, how good their tools are (development IDEs for Java and .NET at least have good built-in tools that make many refactorings simple and safe) and what kind of safety net they have in place to catch mistakes – automated tests, code reviews, static analysis.

Some maintenance teams don’t refactor because they are too afraid of making mistakes. It’s a vicious circle – over time the code will get harder and harder to understand and change, and they will have more reasons to be more afraid. Others claim that a maintenance team is not working correctly if they don’t spend at least 50% of their time refactoring.

The real answer is somewhere in between – enough refactoring to make changes and fixes safe. There are cases where extensive refactoring, restructuring or rewriting code is the right thing to do. Some code is too dangerous to change or too full of bugs to leave the way it is – studies show that in most systems, especially big systems, 80% of the bugs can cluster in 20% of the code. Restructuring or rewriting this code can pay off quickly, reducing problems in production, and significantly reducing the time needed to make changes and test them as you go forward.

Continuous Testing

Testing is even more important and necessary in maintenance than it is in development. And it’s a major part of maintenance costs. Most maintenance teams rely on developers to test their own changes and fixes by hand to make sure that the change worked and that they didn’t break anything as a side effect. Of course this makes testing expensive and inefficient and it limits how much work the team can do. In order to move fast, to make incremental changes and refactoring safe, the team needs a better safety net, by automating unit and functional tests and acceptance tests.

It can take a long time to put in test scaffolding and tools and write a good set of automated tests. But even a simple test framework and a small set of core fat tests can pay back quickly in maintenance, because a lot changes (and bugs) tend to be concentrated in the same parts of the code – the same features, framework code and APIs get changed over and over again, and will need to be tested over and over again. You can start small, get these tests running quickly and reliably and get the team to rely on them, fill in the gaps with manual tests and reviews, and then fill out the tests over time. Once you have a basic test framework in place, developers can take advantage of TFD/TDD especially for bug fixes – the fix has to be tested anyways, so why not write the test first and make sure that you fixed what you were supposed to?

Continuous Integration

To get Continuous Testing to work, you need a Continuous Integration environment. Understanding, automating and streamlining the build and getting the CI server up and running and wiring in tests and static analysis checks and reporting can take a lot of work in an enterprise system, especially if you have to deal with multiple languages and platforms and dependencies between systems. But doing this work is also the foundation for simplifying release and deployment – frequent short releases means that release and deployment has to be made as simple as possible.

Onsite Customer / Product Owner

Working closely with the customer to make sure that the team is delivering what the customer needs when the customer needs it is as important in maintenance as it is in developing a new system. Getting a talented and committed Customer engaged is hard enough on a high-profile development project – but it’s even harder in maintenance. You may end up with too many customers with conflicting agendas competing for the team’s attention, or nobody who has the time or ability to answer questions and make decisions. Maintenance teams often have to make compromises and help fill in this role on their own.

But it doesn’t all fit….

Kilner’s main point of concern isn’t really with Agile methods in maintenance. It’s with incremental design and development in general – that some work doesn’t fit nicely into short time boxes. Short iterations might work ok for bug fixes and small enhancements (they do), but sometimes you need to make bigger changes that have lots of dependencies. He argues that while Agile teams building new systems can stub out incomplete work and keep going in steps, maintenance teams have to get everything working all at once – it’s all or nothing.

It’s not easy to see how big changes can be broken down into small steps that can be fit into short time boxes. I agree that this is harder in maintenance because you have to be more careful in understanding and untangling dependencies before you make changes, and you have to be more careful not to break things. The code and design will sometimes fight the kinds of changes that you need to make, because you need to do something that was never anticipated in the original design, or whatever design there was has been lost over time and any kind of change is hard to make.

It’s not easy – but teams solve these problems all the time. You can use tools to figure out how much of a dependency mess you have in the code and what kind of changes you need to make to get out of this mess. If you are going to spend “weeks, months, or even years” to make changes to a system, then it makes sense to take time upfront to understand and break down build dependencies and isolate run-time dependencies, and put in test scaffolding and tests to protect the team from making mistakes as they go along. All of this can be done in time boxed steps. Just because you are following time boxes and simple, incremental design doesn’t mean that you start making changes without thinking them through.

Read Working With Legacy Code – Michael Feathers walks through how to deal with these problems in detail, in both object oriented and procedural languages. What to do if it takes forever to make a change. How to break dependencies. How to find interception points and pinch points. How to find structure in the design and the code. What tests to write and how to get automated tests to work.

Changing data in a production system, especially data shared with other systems, isn’t easy either. You need to plan out API changes and data structure changes as carefully as possible, but you can still make data and database changes in small, structured steps.

To make code changes in steps you can use Branching by Abstraction where it makes sense (like making back-end changes) and you can protect customers from changes through Feature Flags and Dark Launching like Facebook and Twitter and Flickr do to continuously roll out changes – although you need to be careful, because if taken too far these practices can make code more fragile and harder to work with.

Agile development teams follow incremental design and development to help them discover an optimal solution through trial-and-error. Maintenance teams work this way for a different reason – to manage technical risks by breaking big changes down and making small bets instead of big ones.

Working this way means that you have to put in scaffolding (and remember to take it out afterwards) and plan out intermediate steps and review and test everything as you make each change. Sometimes it might feel like you are running in place, that it is taking longer and costing more. But getting there in small steps is much safer, and gives you a lot more control.
Teams working on large legacy code bases and old technology platforms will have a harder time taking on these ideas and succeeding with them. But that doesn’t mean that they won’t work. Yes, you can be Agile in maintenance.

Tuesday, October 4, 2011

Dealing with security vulnerabilities ... er... bugs

A serious problem in many organizations is that development teams (and their business sponsors) don't take ownership for understanding and managing software security risks, and often try to ignore vulnerabilities or hide them. Without real pressure from the top, it's hard to convince developers and management that dealing with security vulnerabilities is a priority because vulnerabilities aren't requirements or real problems — they are potential problems and risks that can be put off until later.

This is wrong. Vulnerabilities found in pen testing and reviews and scans are either bugs — real problems in the code that should be fixed — or they are noise — false positives or motherhood that can be ignored. Treating them as something different and distinct and managing them in a different way is a mistake.

Read my latest post at the SANS AppSec Street Fighter blog on Dealing with Security Vulnerabilities.
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