SRE Weekly Issue #49

My vacation visiting the Mouse was awesome!  I had a lot of time to work on a little project of mine.  And now I’m back just in time for Black Friday and Cyber-whatever. Good luck out there, everyone!


2016/17 State of On-Call Webinar (with Register to learn what 800+ survey respondents have to say about life on-call.


Another issue of BWH’s Safety Matters, this time about a prescribing accident. The system seems to have been almost designed to cause this kind of error, so it’s good to hear that a fix was already about to be deployed.

This is a great article on identifying the true root cause(s) of an incident, as opposed to stopping with just a “direct cause”. I only wish it were titled, Use These Five Weird Tricks to Run Your RCA!

Etsy describes how they do change management during the holidays:

[…] at Etsy, we still push code during the holidays, just more carefully, it’s not a true code freeze, but a cold, melty mixture of water and ice. Hence, Slush.

This issue of Production Ready is about battling code rot through incrementally refactoring an area of a codebase while you’re doing development work that touches it.

Shutterstock shares some tips they’ve learned from writing postmortems. My favorite part is about recording a timeline of events in an incident. I’ve found that reading an entire chat transcript for an incident can be tedious, so it can be useful to tag items of interest using a chat-bot command or a search keyword so that you can easily find them later.

The “Outage!” AMA happened while I was on vacation, and I still haven’t had a chance to listen to it. Here’s a link in case you’d like to.

My favorite:

If something breaks in production, how do you know about it?

Weaver is a tool to help you identify problems in your microservice consumers by doing “bad” things like responding slowly to a fraction of requests.

Barclays reduced load on their mainframe by adding MongoDB as a caching layer to handle read requests. What the heck does “mainframe” mean in this decade, anyway?

We’d do well to remember during this holiday season that several seconds of latency in web requests is tantamount to an outage.

Tyler Treat gives us an eloquently presented argument for avoiding writing code as much as possible, for the sake of stability.


So far, no big-name Black Friday outages. We’ll see what Cyber Monday has in store.

  • Everest (datacenter)
    • Everest suffered a cringe-worthy network outage subsequent to a power failure. Power came off and on a couple of times, prompting their stacked Juniper routers to assume they’d failed in booting and go into failure recovery mode. Unfortunately, the secondary OS partitions on the two devices contained different JunOS versions, so they wouldn’t stack properly.

      I’d really like to read the RFO on the power outage itself, but I can’t find it. If anyone has a link, could you please send it my way?

  • Argos

SRE Weekly Issue #48

This is the first issue of SRE Weekly going out to over 1000 email subscribers! Thanks all of you for continuing to make my little side project so rewarding and fulfilling. I can’t believe I’m almost at a year.

Speaking of which, there won’t be an issue next week while my family and I are vacationing at Disney World. See you in two weeks!


Downtime sucks. Learn how leading minds in tech respond to outages on the Nov. 16th “Ask Me Anything” from Catchpoint & O’Reilly Media:


A detailed description of Disaster Recovery as a Service (DRaaS), including a discussion of the cost versus creating a DR site oneself. This is the part I always wonder about:

However, for larger enterprises with complex infrastructures and larger data volumes spread across disparate systems, DRaaS has often been too complicated and expensive to implement.

This one’s so short I can almost quote the whole thing here. I love its succinctness:

Regardless of what we discover, we understand and truly believe that everyone did the best job they could, given what they knew at the time, their skills and abilities, the resources available, and the situation at hand.

Just over four years ago, Amazon had a major outage in Elastic Block Store (EBS). Did you see impact? I sure did. Here’s Netflix’s account of how they survived the outage mostly unscathed.

I’m glad to see more people writing that Serverless != #NoOps. This article is well-argued even though it turns into an OnPage ad 3 paragraphs from the end.

What else can we expect from Greater Than Code + Charity Majors? This podcast is 50 minutes of awesome, and there’s a transcription, too! Listen/read for awesome phrases like “stamping out chaos”, find out why Charity says, “I personally hate [the term ‘SRE’] (but I hate a lot of things)”, and hear Conway’s law applied to microservices, #NoOps debunking, and a poignant ending about misogyny and equality.

Microsoft released its Route 53 competitor in late September. They say:

Azure DNS has the scale and redundancy built-in to ensure high availability for your domains. As a global service, Azure DNS is resilient to multiple Azure region failures and network partitioning for both its control plane and DNS serving plane.

This issue of BWH Safety Matters details an incident in which a communication issue between teams that don’t normally work together resulted in a patient injury. This is exactly the kind of pitfall that becomes more prevalent with the move toward microservices, as siloed teams sometimes come into contact only during an incident.

A detailed postmortem from an outage last month. Lots of takeaways, including one that kept coming up: test your emergency tooling before you need to use it.


  • Canada’s immigration site
    • I’m sure this is indicative of something.
  • Office 365
  • Twitter
    • Twitter stopped announcing their AS in BGP worldwide, resulting in a 30-minute outage on Monday.
  • Google BigQuery
    • Google writes really great postmortems! Here’s one for a 4-hour outage in BigQuery on November 8, posted on November 11. Fast turnaround and an excellent analysis. Thanks, Google — we appreciate your hard work and transparency!
  • Pingdom
    • Normally I wouldn’t include such a minor outage, but I love the phrase “unintended human error” that they used. Much better than the intended kind.
  • WikiLeaks
  • eBay

SRE Weekly Issue #47


Downtime sucks. Learn how leading minds in tech respond to outages on the Nov. 16th “Ask Me Anything” from Catchpoint & O’Reilly Media:


Next year, SRECon is expanding to three events: Americas, EMEA, and Asia. The Americas event is also moving from Santa Clara to San Francisco, which I, for one, am especially grateful for. The CFP for SRECon17 Americas just opened up, and proposals are due November 30th, so get cracking! I can’t wait to see what all of you have to share!

I have a somewhat dim view of automated anomaly detection in metrics based on my experience with a few tools, but if Datadog’s algorithms live up to their description, they might really have something worthwhile.

When a responder gets an anomaly alert, he or she needs to know exactly why the alert triggered. The monitor status page for anomaly alerts shows what the metric in question looked like over the alert’s evaluation window, overlaid with the algorithm’s predicted range for that metric.

This issue of Production Ready chronicles Mathias Lafeldt’s effort to create a staging environment. I like the emphasis on using an entirely separate AWS account for staging. This is increasingly becoming a best practice.

What’s causing all that API request latency? Here’s an interesting debug run using Honeycomb. Negative HTTP status codes? Sure, that’s totally a thing, right?

I love this idea: Susan Fowler notes that large, complex systems are constantly changing, and this makes reproducing bugs difficult or impossible. Her suggestion is to log enough that you can logically reconstruct the state of the system at the time the bug occurred. This is the same kind of thing the Honeycomb folks are saying: throw a lot of information into your logs, just in case you might need it to debug something unforeseen.


SRE Weekly Issue #46

This may be the biggest issue to date. Lots of great articles this week, plus updates from the Dyn DDoS, and of course all of the awesome content I held off on posting last week.


Tell the world what you think about being on-call. Participate in the annual State of On-Call Survey.


I’ve linked to several posts on Etsy’s Code as Craft blog in the past, and here’s another great one. Perhaps not the typical SRE article you might have been expecting me to link to, but this stuff is important in every tech field, including SRE. We can’t succeed unless every one of us has a fair chance at success.

In 2014, CodeSpaces suffered a major security breach that abruptly ended their business. I’d say that’s a pretty serious reliability risk right there, showing that security and reliability are inextricably intertwined.

Check it out! Catchpoint is doing another Ask Me Anything, this time about incident response. Should be interesting!

My fellow Heroku SRE, Courtney Eckhardt, expanded on a section of our joint SRECon talk for this session at OSFeels. She had time for Q&A, and there were some really great questions!

Mathias rocks it, as usual, in this latest issue of Production Ready.

Netflix has released a new version of Chaos Monkey with some interesting new features.

Scalyr worked with Mathias Lafeldt to turn his already-awesome pair of articles into this excellent essay. He brings in real-world examples of major outages and draws conclusions based on them. He also hits on a number of other topics he’s written about previously. Great work, folks!

How many times have you pushed out a puppet change that you tested very thoroughly, only to find that it did something unexpected on a host you didn’t even think it would apply to? Etsy’s solution to that is this tool that shows catalog changes for all host types in your fleet in a diff-style format.

“We ended up 50 percent over our worst case after day one, we figured this was going to be bad within six hours”

It’s pretty impressive to me that Niantic managed to keep Pokemon Go afloat as well as they did. They worked very closely with Google to grow their infrastructure much faster than they had planned to.

As Spotify has grown to 1400 microservices and 10,000 servers, they’ve moved toward a total ownership model, in which development teams are responsible for their code in production.

Pingdom suffered a major outage during the Dyn DDoS, not only due to their own DNS-related issues, but also due to the massive number of alerts their system was trying to send out to notify customers that their services were failing.

[…] at 19:20 we went to DEFCON 1 and suspended the alerting service altogether.

Here’s Dyn’s write-up of the DDoS.

As they promised, here’s PagerDuty’s root cause analysis from the Dyn DDoS.

This is a pretty great idea. Ably has written their client libraries to reach their service through a secondary domain if the primary one is having DNS issues. Interestingly, their domain,, was also impacted by the .io TLD DNS outage (detailed below) just days after they wrote this. gives us some really interesting numbers around the Dyn DDoS, based on status posts made by their customers.  I wonder, was it really the largest in history?

Here’s a nice write-up of day one of ServerlessConf, with the theme, “NoOps isn’t a thing”.

Not a magic bullet, but still pretty interesting.

[…] it allows you to incrementally replicate live Virtual Machines (VMs) to the cloud without the need for a prolonged maintenance period. You can automate, schedule, and track incremental replication of your live server volumes, simplifying the process of coordinating and implementing large-scale migrations that span tens or hundreds of volumes.

Earlier this year, Australia’s online census site suffered a major outage. Here’s a little more detail into what went wrong. TL;DR: a router dropped its configuration on reboot. has put in place a lot of best practices in incident response and on-call health.

After extensive rationalisation, GOV.UK have reached a stage where only 6 types of incidents can alert (wake them up) out of hours. The rest can wait until next morning.

Unfortunately, I’m guessing one of those six types happened this week, as you can see in the Outages section below.


  • .io TLD
    • The entire .io top-level domain went down, resulting in impact to a lot of trendy companies that use *.io domains. It doesn’t matter how many DNS providers you have for your domain if your TLD’s nameservers aren’t able to give out their IPs. Worse yet, .io‘s servers sometimes did respond, but with an incorrect NXDOMAIN for valid domains. .io‘s negative-caching TTL of 3600 seconds made this pretty nasty.

      On the plus side, this outage provided the last piece in the puzzle in answering my question, “does ‘fast-fluxing’ your DNS providers really work?”. Answer: no. I’ll write up all of my research soon and post a link to it here.

  • The Pirate Bay
  • California DMV
  • AT&T
  • British Telecom
  • PlayStation Network

SRE Weekly Issue #45

This past Friday, it was as if Oprah were laughing maniacally, shouting, “You get an outage, and you get an outage, EVERYONE GETS AN OUTAGE!” Hat-tip to all of you who spent the day fighting fires like I did.

I’ve decided to dedicate this week’s issue entirely to the incident, the fallout, and information on redundant DNS solutions. I’ll save all of the other great articles from this week for the next issue.


Tell the world what you think about being on-call. Participate in the annual State of On-Call Survey.


The Register has a good overview of the attacks.

Dyn released this statement on Saturday with more information on the outage. Anecdotally (based on my direct experience), I’m not sure their timeline is quite right, as it seems that I and others I know saw impact later than Dyn’s stated resolution time of 1pm US Eastern time. Dyn’s status post indicates resolution after 6pm Eastern, which matches more closely with what I saw.

Among many other sites and services, AWS experienced an outage. They posted an unprecedented amount of detail during the incident in a banner on their status site. Their status page history doesn’t include the banner text, so I’ll quote it here:

These events were caused by errors resolving the DNS hostnames for some AWS endpoints. AWS uses multiple DNS service providers, including Amazon Route53 and third-party service providers. The root cause was an availability event that occurred with one of our third-party DNS service providers. We have now applied mitigations to all regions that prevent impact from third party DNS availability events.

Nice job with the detailed information, AWS!

Krebs on Security notes that the attack came hours after a talk on DDoS attacks at NANOG. Krebs was a previous target of a massive DDoS, apparently in retaliation for his publishing of research on DDoS attacks.

Paging through PagerDuty was down or badly broken throughout Friday. Many pages didn’t come through, and those that did sometimes couldn’t be acknowledged. Some pages got stuck and PagerDuty’s system would repeatedly call engineers and leave the line silent. [source: personal experience] Linked is PagerDuty’s “Initial Outage Report”. It includes a preliminary explanation of what went wrong, an apology, and a pledge to publish two more posts: a detailed timeline and a root cause analysis with remediation items.

Sumo Logic implemented dual nameserver providers after a previous DNS incident. This allowed them to survive the Dyn outage relatively unscathed.

Anonymous and New World Hackers have claimed responsibility for Friday’s attack, but that claim may be suspect. Their supposed reasons were to “retaliate for the revocation of Julian Assange’s Internet access” and to “test their strength”.

WikiLeaks bought their claim and asked supporters to cut it out.

A great basic overview of how recursive DNS queries work, published by Microsoft.

A much more detailed explanation if how DNS works. Recursive and iterative DNS queries are covered in more depth, along with AXFR/IXFR/NOTIFY which can be used to set up a redundant secondary DNS provider for your domain.

Heroku was among many sites impacted by the attack. Heroku’s status site was also impacted, prompting them to create a temporary mirror. This is painfully reminiscent of an article linked two issues ago about making sure your DNS is redundant.

Full disclosure: Heroku is my employer.

EasyDNS has this guide on setting up redundant DNS providers to safeguard against an attack like this. However, I’m not sure about their concept of “fast fluxing” your nameservers, that is, changing your nameserver delegation with your registrar when your main DNS provider is under attack.

Unless I’m mistaken, a change in nameservers for a domain can take up to 2 days (for .com) to be seen by all end-users, because their ISP’s recursive resolver could have your domain’s NS records cached, and the TTL given by the .com nameservers is 2 days.

Am I missing something? Maybe recursive resolvers optimistically re-resolve your domain’s NS records if all of your nameservers time out or return SERVFAIL? If you know more about this, please write to me!


I’m not going to bother naming all of the many sites and services that went down on Friday, because there were too many and I’d inevitably miss some. The below outages all occurred earlier in the week.

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