May 21, 2024


All service engineering groups in Azure are already acquainted with postmortems as a device for higher understanding what went fallacious, the way it went fallacious, and the client affect of the associated outage. An vital a part of our postmortem course of is for all related groups to create restore gadgets aimed toward stopping the identical sort of outage from taking place once more, however whereas reactive approaches can yield outcomes, we needed to maneuver this to the left—approach left. We needed to get higher at uncovering dangers earlier than that they had an affect on our prospects, not after. For immediately’s put up in our Advancing Reliability weblog sequence I’ve requested Richie Costleigh, Principal Program Supervisor from our Azure downside administration workforce, to share insights into our journey as we work in direction of advancing our postmortem and resiliency menace modeling processes.”—Mark Russinovich, CTO, Azure


At a excessive degree, our aim is to keep away from self-inflicted and/or avoidable outages, however much more instantly, our aim is to have the ability to cut back the probability of affect to our prospects as a lot as potential. On this context, an outage is any incident during which our providers fail to satisfy the expectations of (or negatively affect the workloads of) our prospects, each internally and externally. To keep away from that, we wanted to enhance how we uncover dangers earlier than they affect buyer workloads on Azure. However Azure itself is a big, advanced distributed system—how ought to we method resiliency menace modeling if our group provides hundreds of options, comprised of tons of of “providers,” every with a workforce of 5 to 50 engineers, distributed throughout a number of completely different components of the group, and every with their very own processes, instruments, priorities, and targets? How will we scale our resiliency menace modeling course of out, and cause throughout all these particular person danger assessments? To deal with these challenges, it took some main adjustments to affix the reactive method with the extra proactive method.

Beginning our journey

We began the shift left with a premortem pilot program. We seemed again at previous outages and developed a questionnaire that helped not solely to begin discussions but additionally to supply a construction to them. Subsequent, we chosen a number of providers of various goal and structure—every time we sat down with a workforce, we discovered one thing new, received higher and higher at figuring out dangers, integrated suggestions from the groups on the method, then tried once more with the subsequent workforce. Ultimately, we began to establish the best inquiries to ask in addition to different parts we wanted to make this course of productive and impactful. A few of these parts already existed, others wanted to be created to assist a centralized method to resiliency menace modeling. Many who existed additionally required adjustments or integration into an total answer that met our targets. What follows is a high-level overview of our method, and the weather we found had been essential to proceed bettering the area.

We created a tradition of steady and fearless danger documentation

We realized that there would must be a big up-front funding to search out out the place our dangers had been. Thorough premortems take time—the dear and “in excessive demand” engineer form of time, the “we’re working inside a good timeline to ship buyer worth and may’t cease to do that” type of engineer time. Typically we wanted to assist them perceive that, despite the fact that their service solely had one outage in two years, there are dozens of different providers within the dependency chains of our options which have additionally solely had one outage prior to now two years. The purpose is that, from our prospects’ perspective, they’ve seen greater than “simply” two outages.

We needs to be skeptical that low danger is one thing we are able to safely ignore. We should embark on wholesome, fearless looking stock of dangers to outages. We would have liked a course of that not solely helps detailed discussions of lingering points, and an evaluation of the dangers with out concern of reprisal, but additionally informs investments in frequent options and mitigations that may be leveraged broadly throughout a number of providers in a large-scale group consisting of tons of or hundreds of providers.

Our aim is a steady seek for dangers, and to have “residing dangers” menace fashions as an alternative of static fashions which are solely up to date each X months. As soon as the preliminary funding to search out that preliminary set of dangers lands, we needed to maintain issues updated with a well-defined course of. The important thing at first was to not be deterred by how massive the preliminary funding “moat” was, between us and our targets. The true profit we see now’s that danger assortment is constructed into our tradition. This allows dangers to be collected from many numerous sources and constructed into our organizational processes.

So, how greatest to begin the method of figuring out dangers?

We used each reactive and proactive approaches to uncovering dangers

We leveraged our postmortem evaluation program

Whereas searching for dangers, it is smart to have a look at what has occurred prior to now and search for clues to what can occur once more sooner or later. A strong postmortem evaluation program was key on this regard. We already had a workforce that analyzed postmortems, searching for frequent themes and surfacing them for deeper evaluation and to tell investments. Their analyses helped us not solely route groups to high quality applications or initiatives that would assist tackle the chance, but additionally highlighted the necessity for different investments we didn’t know we wanted till we noticed how prevalent the chance was. The sorts of danger classes they recognized from postmortem evaluation turned a subset of our focus areas once we seemed for dangers that had not occurred but. It’s value noting right here that postmortem evaluation is simply nearly as good because the postmortem itself.

We leveraged our postmortem high quality evaluation program

The standard of a postmortem determines its usefulness, subsequently we invested in a Postmortem High quality Evaluate Program. Steering was printed, coaching was made out there, and a big pool of reviewers would price every “excessive affect” outage postmortem after it was written. Postmortems that had low scores or wanted extra readability had been despatched again to the authors. Excessive affect postmortems are reviewed weekly in a gathering that features engineers from different groups and senior leaders, each of whom ask questions and provides suggestions round the best motion plans. Having this program vastly elevated our capability to be taught from and act on postmortem information.

Nonetheless, we knew that we couldn’t restrict our seek for dangers to the previous.

We received higher at premortems to be extra proactive

Some might have heard the time period “premortem,” which is an identical course of to a Failure Mode Evaluation (FMA).

In line with the Harvard Enterprise Evaluate (September 2007, Situation 1), “A premortem is the hypothetical reverse of a postmortem. A postmortem in a medical setting permits well being professionals and the household to be taught what induced a affected person’s loss of life. Everybody advantages besides, after all, the affected person. A premortem in a enterprise setting comes at first of a venture moderately than the top in order that the venture might be improved moderately than autopsied. In contrast to a typical critiquing session, during which venture workforce members are requested what may go fallacious, the premortem operates on the idea that the “affected person” has died, and so asks what did go fallacious. The workforce members’ job is to generate believable causes for the venture’s failure.”

Within the context of Azure, the aim of a premortem is to foretell what might go fallacious, establish the potential dangers, and mitigate or take away them earlier than the set off occasion ends in an outage. In line with How you can Catch a Black Swan: Measuring the Advantages of the Premortem Approach for Threat Identification, premortem methods can establish extra high quality dangers and suggest extra high quality adjustments; it’s a simpler danger administration method in contrast with others.

Conducting a premortem shouldn’t be a really tough endeavor, however you should be positive you contain the best set of individuals. For a selected buyer answer, we gathered probably the most educated engineers for that answer and, even higher, introduced the brand new ones to allow them to be taught. Subsequent, we had them brainstorm as many causes as potential why they could be woken up at four:00 AM as a result of their prospects are experiencing an outage that they need to mitigate. We like to begin with a hypothetical query, “Think about you had been away on trip for 2 weeks and got here again listening to that your service had an outage. Earlier than you discover out what the contributing elements had been for that outage, try and listing as many issues as potential you suppose may very well be the doubtless causes.” Every of these was captured as a danger, together with documenting the triggers that trigger the outage, the affect on prospects, and the probability of it taking place.

After we recognized the dangers, we wanted to have an motion plan to handle them.

We created “Threat Risk Fashions”

If premortem is the looking and fearless stock of dangers, the chance menace mannequin is what combines that with the motion plan. In case your workforce is doing failure mode evaluation or common danger critiques, this effort needs to be easy. The chance menace mannequin takes your listing of dangers and builds in what you anticipate to do to scale back buyer ache.

After we recognized the dangers, we wanted to have a standard understanding of the best fixes in order that these patterns may very well be used all over the place there was an identical danger. If these fixes are long-term, we requested ourselves “what can we do within the meantime to scale back the probability or affect to our prospects”? Listed here are a number of the questions we requested:

  • What telemetry exists to acknowledge the chance when it’s triggered? 
  • What if this occurs tomorrow? What guardrails or processes are in place till the ultimate repair is accomplished?
  • How lengthy does it take to do that interim mitigation and is it automated? Can or not it’s automated? Why not?
  • Has the mitigation been examined? When was the final time you examined it?
  • What have you ever achieved to make sure you have added probably the most resiliency potential, as an example, in case your essential dependencies have an outage? Have you ever labored with that dependency to make sure you are following their steerage and utilizing their newest libraries?
  • Are there any locations the place you’ll be able to ask for a rise in COGS to be extra resilient?
  • What mitigations are you not doing because of the value or complexity or since you should not have the sources?

Threat Mitigation Plans had been documented, aligned with frequent options, and tracked. Any groups that indicated the mitigations would want extra builders or cash to implement wanted mitigations had been offered a discussion board to ask for it within the context of resiliency and high quality. Work gadgets had been created for all of the duties wanted to make the service as resilient as potential and linked to the dangers we documented so we might comply with up on their completion.

However how do we all know we’re precluding the chance appropriately? How do we all know what the “proper” mitigation methods are? How might we cut back the quantity of labor it took, and forestall everybody from fixing the identical downside in a customized approach?

We created a centralized repository of all dangers throughout all providers

Dangers Risk Fashions are simpler when captured and analyzed centrally

If each workforce went off and analyzed their postmortems, carried out a premortem, created a danger menace mannequin, after which documented all the pieces individually there is no such thing as a doubt we’d have the ability to cut back the variety of outages now we have. Nonetheless, by not having a approach for groups to share what they discovered with others, we’d have missed alternatives to know broader patterns within the danger information. Dangers in a single service had been usually dangers in different providers as properly, however for one cause or one other, it didn’t make it into the chance menace fashions of all providers that had been in danger. We additionally wouldn’t have observed that unfinished repairs or dangers in a single service are dangers to different providers. We’d have missed the prospect to doc patterns that can stop this danger from showing elsewhere when a brand new service is spun up. We’d not have realized that the scope of a premortem shouldn’t be restricted to particular person service boundaries, however moderately achieved throughout all of the providers that work collectively for a selected buyer situation. We’d have missed alternatives to suggest frequent mitigation methods and spend money on broad efforts to handle mitigations at scale utilizing the identical mitigation plan. Briefly, we’d have missed many alternatives to tell quite a few investments throughout service boundaries.

We applied a standard approach of categorizing dangers

In some circumstances, we knew we wanted to know what “sorts” of dangers we had been discovering. Had been they Single Factors of Failure? Insufficiently configured throttling? To that finish, we created a hierarchical system of shorthand “tags” that had been used to explain classes of points on which we needed to focus. These tags had been used for analyzing postmortems to establish frequent patterns, in addition to marking particular person dangers in order that we might higher look throughout dangers in the identical classes to establish the best motion plans.

We had common critiques of the Threat Risk Fashions

Having the finished Threat Risk Fashions enabled us to schedule critiques in entrance of senior management, architects, members of the devoted cross-Azure High quality Staff, and others. These conferences had been extra than simply critiques, they offered a chance to come back collectively as a various workforce to establish areas for which we wanted frequent options, mitigations, and follow-up actions. Motion gadgets had been collected, homeowners assigned, and dangers had been then linked with the motion plans so we might comply with up down the street to find out how groups progressed.

All of it got here collectively, time to take it to the subsequent degree and do that for tons of of providers!

In abstract, it took extra than simply spinning up a program to establish and doc dangers. We would have liked to encourage, but additionally have the best processes in place to get probably the most out of that effort. It took coordination throughout many applications and the creation of many others. It took plenty of cross-service-team communication and dedication.

Accelerating the resiliency menace modeling Program has already yielded many advantages for our essential Azure providers, so we will probably be increasing this course of to cowl each service in Azure. To this finish, we’re constantly refining our course of, documentation, and steerage in addition to leveraging previous danger discussions to handle new dangers. Sure, this can be a lot of labor, and there’s no silver bullet, and we’re nonetheless bringing increasingly more sources into this effort, however in terms of reliability, we imagine in “go massive”! 


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