After yet another cloud outage yesterday (see AWS’s S3 outage was so bad Amazon couldn’t get into its own dashboard to warn the world) the world (or at least its North American part) once again went crazy how dangerous the cloud is and how you should go build your own data center because you know better what is good for your business.

Putting aside all the hype as well as some quite senseless social media posts about AWS SLAs, here is our thought process for developing highly available cloud services or more importantly making conscious decisions what our services’ SLAs should be.

I will base this post on my customer experience with Docker that was impacted by the outage yesterday but also walk you through the thought process for our own services. Without knowing Dockers business strategy I will speculate a bit but my goal is to walk you through the process and not define Docker’s HA strategy. For those who are not familiar what the problem with Docker was, Docker’s public repository is hosted on S3 and was not accessible during the outage.

The first thing we look at is, of course, the business impact of the service. Nothing new here! Thinking about Docker’s registry outage here are my thoughts:

  • An outage may impact all customer deployments that use Docker Hub images. Theoretically, this is every one of Docker’s customers. Based on this only the impact can be huge
  • On the other side though Docker’s enterprise (small and big) customers customize the images they use and most probably store them in private repositories. Docker’s outage doesn’t necessarily impact those private repositories, which means that we can lower the impact
  • Docker is a new company though and their success is based on making developers happy. Those developers may be constantly hacking something (like for example my case yesterday:)) and using the public repository. Being down will make the developers unhappy and will have an impact on Docker’s PR
  • In addition, Docker wants to establish itself as THE company for the cloud. Incidents like yesterday’s may have a negative impact on this inspiration mainly from PR and growth point of view

With just those simple points, one can now make a conscious decision that the impact of Docker’s public repository being down is most probably high. What to do about it?

The simplest thing you can do in such a situation is to set the expectations upfront. Calculate a realistic availability SLA and publish it on your site. Unfortunately, looking at Docker Hub’s site I was not able to find one. In general, I think cloud providers bury their SLAs so deep that it is hard for customers to find them. Thus, people search on Google or Bing and start citing the first number they find (relevant or not), which makes the PR issue even worse. I would go even further – I would publish not only the 9s of my SLA but also what those 9s equate to in time, and whether this is per week, month or year. Taking, for example, the Amazon’s S3 SLA, after being down for approximately 3 hours yesterday, if we consider it annually, they are still within their 8h 45min allowed downtime.

Now, that you made sure that you have a good answer to your customers, let’s think how can you make sure that you keep those SLAs intact. However, this doesn’t mean that you should go ahead and overdesign your infrastructure and spin up a multimillion project that will provide redundancy for every component of every application you manage. There were a lot of voices we’ve heard yesterday calling for you to start multi-cloud deployments immediately. You could do that but is this the right thing?

I personally like to think about this problem gradually and revisit the HA strategy on a regular basis. During those reviews, you should look at the business requirements as well as what is the next logical step to make improvements. Multi-cloud can be in your strategy long term but this is certainly much bigger undertaking than providing quick HA solution with your current provider. In yesterday’s incident, the next logical step for Docker would be to have a second copy of the repository in US West and ability to quickly switch to it if something happens with US East (or vice versa). This is a small incremental improvement that will make a huge difference for the customers and boost Docker’s PR because they can say: “Look! we host our repository on S3 but their outage had minimal or no impact on us. And, by the way, we know how to do this cloud stuff.” After that, you can think about multi-cloud and how to implement it.

Last, but not least your HA strategy should be also tied to your monitoring, alerting, remediation but also to your customer support strategy. Monitoring and alerting is clear – you want to know if your site or parts of it are down and take the appropriate actions as described in your remediation plan. But why, your customer support strategy? Well, if you haven’t noticed – AWS Service Dashboard was also down yesterday. The question comes up, how do you notify your customers of issues with your service if your standard channel is also down? I know that lot of IT guys don’t think of it but Twitter turns out a pretty good communication tool – maybe you should think of it next time your site is down.

Developing solid HA strategy doesn’t need to be a big bang approach. As everything else, you should ask good questions, do incremental steps, fail and learn. And most importantly, take responsibilities for your decision and don’t blame the cloud for all bad things that happen with your site.

Recently I had to design the backup infrastructure for cloud workloads for a client in order to ensure that we comply with the Business Continuity and Disaster Recovery standards they have set. However, following traditional IT practices in the cloud quite often poses certain challenges. The scenario that we had to satisfy is best shown in the picture below:

Agent-Based Backup Architecture

The picture is quite simple:

  1. Application servers have a backup agent installed
  2. The backup agent submits the data that needs to be backed up to the media server in the cloud
  3. The cloud media server submits the data to the backup infrastructure on premise, where the backups are stored on long-term storage according to the policy

This is a very standard architecture for many of the current backup tools and technologies.

Some of the specifics in the architecture above are that:

  • The application servers and the cloud media server exist in different accounts or VPCs if we use AWS terminology or virtual networks or subscriptions if you consider Microsoft Azure terminology
  • The connectivity between the cloud and on-premise is established through DirectConnect or ExpressRoute and logically those are also considered separate VPCs or virtual networks

This architecture would be perfectly fine if the application servers were long-lived, however, we were transitioning the application team to a more agile DevOps process, which meant that they will use automation to replace the application servers with every new deployment (for more information take a look at the Blue/Green Deployment White Paper published on our company’s website). This, though, didn’t fit well with the traditional process that the IT team, managing the on-premise Netbackup infrastructure, uses.  The main issue was that every time one of the application servers gets terminated, somebody from the on-prem IT team will get paged for failed backup, and trigger an unnecessary investigation.

One option for solving the problem, presented to us by the on-premise IT team, was to use traditional job scheduling solutions to trigger script that will create the backup and submit it to the media server. This approach doesn’t require them to manually whitelist the IP addresses of the application server into their centralized backup tool, and will not generate error event but involved additional tools that would require much more infrastructure and license fees. Another option was to keep the old application servers running longer so that the backup team has enough time to remove the IPs from the white-list. This, though, required manual intervention on both sides (ours and the on-prem IT team) and was prone to errors.

The approach we decided to go with required a little bit more infrastructure but was fully automatable and was relatively cheap compared to the other two options. The picture below shows the final architecture.

The only difference here is that instead of running the backup agents on the actual application instances, we run just one backup agent on a separate instance that has an unlimited lifespan and doesn’t get terminated with every release. This can be a much smaller instance than the ones used for hosting the application, which will save some cost, and its role is only for hosting the backup agent, hence no other connections to it should be allowed. The daily backups for the applications will be stored on a shared drive that is accessible on the instance hosting the agent, and this shared drive is automatically mounted on the new instances during each deployment. Depending on whether you deploy this architecture in AWS or Azure, you can use EFS or Azure Files for the implementation.

Here are the benefits that we achieved with this architecture:

  • Complete automation of the process that supports Blue/Green deployments
  • No changes in the already existing backup infrastructure managed by the IT team using traditional IT processes
  • Predictable, relatively low cost for the implementation

This was a good case study where we bridged the modern DevOps practices and the traditional IT processes to achieve a common goal of continuous application backup.