What is high availability? How does high availability architecture look like? How to set up highly available Kubernetes clusters and applications?
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The article that follows is an extract from the last chapter of The DevOps 2.2 Toolkit: Self-Sufficient Docker Clusters book. It provides a good summary into the processes and tools we explored in the quest to build a self-sufficient cluster that can (mostly) operate without humans.
We split the tasks that a self-sufficient system should perform into those related to services and those oriented towards infrastructure. Even though some of the tools are used in both groups, the division between the two allowed us to keep a clean separation between infrastructure and services running on top of it.
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A self-sufficient system is a system capable of healing and adaptation. Healing means that the cluster will always be in the designed state. As an example, if a replica of a service goes down, the system needs to bring it back up again. Adaptation, on the other hand, is about modifications of the desired state so that the system can deal with changed conditions. A simple example would be increased traffic. When it happens, services need to be scaled up. When healing and adaptation are automated, we get self-healing and self-adaptation. Together, they both a self-sufficient system that can operate without human intervention.
How does a self-sufficient system look? What are its principal parts? Who are the actors?
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I have so much chaos in my life, it’s become normal. You become used to it. You have just to relax, calm down, take a deep breath and try to see how you can make things work rather than complain about how they’re wrong.
— Tom Welling
Monitoring many services on a single server poses some difficulties. Monitoring many services on many servers requires a whole new way of thinking and a new set of tools. As you start embracing microservices, containers, and clusters, the number of deployed containers will begin increasing rapidly. The same holds true for servers that form the cluster. We cannot, anymore, log into a node and look at logs. There are too many logs to look at. On top of that, they are distributed among many servers. While yesterday we had two instances of a service deployed on a single server, tomorrow we might have eight instances deployed to six servers. The same holds true for monitoring. Old tools, like Nagios, are not designed to handle constant changes in running servers and services. We already used Consul that provides a different, not to say new, approach to managing near real-time monitoring and reaction when thresholds are reached. However, that is not enough. Real-time information is valuable to detect that something is wrong, but it does not give us information why the failure happened. We can know that a service is not responding, but we cannot know why.
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Organizations which design systems … are constrained to produce designs which are copies of the communication structures of these organizations” - M. Conway
Many will tell you that they have a scalable system. After all, scaling is easy. Buy a server, install WebLogic (or whichever other monster application server you’re using) and deploy your applications. Then wait for a few weeks until you discover that everything is so “fast” that you can click a button, have some coffee, and, by the time you get back to your desk, the result will be waiting for you. What do you do? You scale. You buy few more servers, install your monster applications servers and deploy your monster applications on top of them. Which part of the system was the bottleneck? Nobody knows. Why did you duplicate everything? Because you must. And then some more time passes, and you continue scaling until you run out of money and, simultaneously, people working for you go crazy. Today we do not approach scaling like that. Today we understand that scaling is about many other things. It’s about elasticity. It’s about being able to quickly and easily scale and de-scale depending on variations in your traffic and growth of your business, and that, during that process, you should not go bankrupt. It’s about the need of almost every company to scale their business without thinking that IT department is a liability. It’s about getting rid of those monsters.
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Today is an exciting day for me. I just decided that the book I spent the last eight months writing is ready for general public.
What made me write the book? Certainly not the promise of wealth since, as any author of technical books will confirm, there is no money that can compensate the number of hours involved in writing a technical book. The reasons behind this endeavor are of a different nature. I realized that this blog is a great way for me to explore different subjects and share my experience with the community. However, due to the format, blog posts do not give enough space to explore, in more details, subjects I’m passionate about so, around eight months ago, I decided to start working on The DevOps 2.0 Toolkit: Automating the Continuous Deployment Pipeline with Containerized Microservices book. It treats similar subjects as those I write about in this blog, but with much more details. More importantly, the book allowed me to organize my experience into a much more coherent story.
The book is about different techniques that help us architect software in a better and more efficient way with microservices packed as immutable containers, tested and deployed continuously to servers that are automatically provisioned with configuration management tools. It’s about fast, reliable and continuous deployments with zero-downtime and ability to roll-back. It’s about scaling to any number of servers, designing self-healing systems capable of recuperation from both hardware and software failures and about centralized logging and monitoring of the cluster.
In other words, this book envelops the whole microservices development and deployment lifecycle using some of the latest and greatest practices and tools. We’ll use Docker, Kubernetes, Ansible, Ubuntu, Docker Swarm and Docker Compose, Consul, etcd, Registrator, confd, Jenkins, and so on. We’ll go through many practices and, even more, tools.
At this moment, around 70% is finished and you’ll receive regular updates if you decide to purchase the book. The truth is that my motivation for writing the book is the same as with this blog. I like sharing my experience and this book is one more way to accomplish that. You can set your own price and if you feel that the minimum amount is still too high, please send me a private message and I’ll get back to you with a free copy.
Please give The DevOps 2.0 Toolkit: Automating the Continuous Deployment Pipeline with Containerized Microservices a try and let me know what you think. Any feedback is welcome and appreciated.
Before we jump and try to explore the practices we must master in order to successfully implement microservices architecture, let us briefly refresh our understanding of monolithic applications.
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In The History of Failed Initiatives I mentioned that microservices as a concept existed for a long time. And yet, most of those who tried organizing their architecture around microservices failed or, to use different words, realized that benefits are shadowed by the increase in complexity (especially in operations). The spark that was born long ago became a star only recently. In order to understand why microservices became a hot topic not long ago, we need to understand better why they failed in the past. The explanation is simple. We neither had the tools nor understood the logic we had to apply. Do we have the tools today? Are we capable of putting in place the right procedures and have the mindset microservices require. I’d say yes, we have and we do. When I say we I mean people with the will and resources to make this happen. As in most other cases, once something new is proven and adopted by some, years need to pass until that something is applied by many. The good news is that I think that we are getting there and, slowly, the more conservative part of the industry (in other words, most of it) is starting to at least consider microservices as an option. Even Gartner had positive words for it. And when Gartner says jump, enterprise jumps.
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I worked with many different clients. From small greenfield projects all the way to big ones in sectors like automotive, lottery, banking, insurance and other industries. With few exceptions teams in those projects can be divided into those that started anew and think that they are using latest and greatest ways to develop and those that are in charge of bigger projects that started long time ago. The later group tends to put to much energy trying to stay afloat that latest and greatest is very low on their list of priorities.
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Microservices are becoming more and more popular and many are choosing to transition away from monolithic architecture. However, this approach was mostly limited to back-end services. While it made a lot of sense to split them into smaller independent pieces that can be accessed only through their APIs, same did not apply to front-end. Why is that? I think that the answer lies in technologies we’re using. The way we are developing front-end is not designed to be split into smaller pieces.
Server-side rendering is becoming history. While enterprise might not agree with that statement and continues pushing for server-side frameworks that “magically” transform, for example, Java objects to HTML and JavaScript, client frameworks will continue to increase in popularity slowly sending server-side page rendering into oblivion. That leaves us with client-side frameworks. Single-Page Applications are what we tend to use today. AngularJS, React, ExtJS, ember.js and others proved to be a next step in evolution of front-end development. However, Single-Page Applications or not, most of them are promoting monolithic approach to front-end architecture.
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