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I know that the Cloud Native / Kubernetes communities have a wealth of experience, and I want to hear about yours! 8 | 9 | [Submit an issue](https://github.com/arschles/kube-best-practices/issues/new) or 10 | [Submit a pull request](https://github.com/arschles/kube-best-practices/compare) to tell me all about it. 11 | 12 | Let's get to it... 13 | 14 | # Observability is golden 15 | 16 | Kubernetes schedules your pods, and is more effective at doing so when it knows: 17 | 18 | - What your pods need 19 | - So tell it this information by adding resource limits 20 | - What is going on with your pods 21 | - So make sure you have good liveness and readiness checks 22 | 23 | 24 | At the same time, _you_ need to know what is going on with your pods, as they change over time. So make sure your [logging](https://www.fluentd.org/), [tracing](http://opentracing.io/), [monitoring](https://prometheus.io/) is in place, so you can observe what's going on. 25 | 26 | # When all else fails, crash 27 | 28 | Crash-only architectures mean that your software should just crash instead of trying to recover more gracefully. 29 | 30 | [Erlang](https://en.wikipedia.org/wiki/Erlang_(programming_language)) popularized this concept because it introduced a [supervisor](http://erlang.org/doc/man/supervisor.html) principle. The supervisor watches over your code (called a process) and restarts it if it crashes. This architecture encourages you to simply crash if something goes wrong, because you know you'll be restarted and can try again. 31 | 32 | If you run in Kubernetes, Kubernetes itself is the "supervisor." Instead of building retry loops or other recovery logic into your app, simply crash and let Kubernetes restart your pod. 33 | 34 | # Unordered is better than ordered 35 | 36 | Whether you like it or not, your app is a distributed system. You can no longer think of it as a single process (even if you're just running one pod, because the pod can move, crash, etc...). One implication of this fact, among many others, is that it's _hard_ to rely on a specific ordering of events. 37 | 38 | [Much](https://amturing.acm.org/p558-lamport.pdf) [research](https://scholar.google.com/scholar?q=ordering+in+distributed+systems&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjW0aXfjffXAhUE8IMKHVOnBgcQgQMIJzAA) has been done on the topic of ordering in distributed systems, so if your app needs to rely on ordered events, you need to understand at least the basic ideas (causal ordering, wall clock ordering, etc...), decide what kind of ordering your app needs, implement it, and then test to make sure it adheres to the definition. 39 | 40 | Alternatively, you can avoid ordering altogether and/or use the Kubernetes primitives to take care of it for you. Examples of these primitives: 41 | 42 | - [Distributed locks](https://github.com/pulcy/kube-lock) 43 | - [Leader election](http://blog.kubernetes.io/2016/01/simple-leader-election-with-Kubernetes.html) 44 | - [Init containers](https://kubernetes.io/docs/concepts/workloads/pods/init-containers/) 45 | 46 | # Loose coupling is better than tight coupling 47 | 48 | As we know, Kubernetes is "always on" and watching over your app. If something changes, it adapts to the change and modifies your app's deployment accordingly to account for the change and bring it back to the state you want it to be in (this is called reconciliation). 49 | 50 | Your app needs to tolerate that dynamism. 51 | 52 | This fact means a wide variety of things: 53 | 54 | - Do not rely on specific pods to be running 55 | - Talk to pods via `Service`s or a service mesh 56 | - Crash if you cannot get a resource or talk to a pod (i.e. crash only software) 57 | - If you need to look for a Kubernetes resource via `kubectl`, the API, or something else, query it by labels, not the name 58 | 59 | # But tight coupling isn't _always_ wrong 60 | 61 | The "atom" of deployment is a `Pod` in Kubernetes, and pods can have more than one container. This design allows for tight coupling between containers - either they all will be running or none will be running. 62 | 63 | So, if you have components of your app that are tightly coupled (e.g. legacy systems, "sidecars", etc...), run them all in containers in the same pod. 64 | 65 | We see this topology in many cases, including: 66 | 67 | - [Envoy](https://www.envoyproxy.io/) as a sidecar to your app - your app talks to `localhost` to access the service mesh 68 | - The [Fluentd logging driver](https://docs.docker.com/engine/admin/logging/fluentd/) runs as a sidecar, and your app is configured to send logs to `localhost` 69 | - A metrics system you may have runs as a sidecar, and your app sends metrics to `localhost` 70 | 71 | # Record your configuration 72 | 73 | Kubernetes provides a [declarative API](https://en.wikipedia.org/wiki/Declarative_programming) that allows you to tell it the _end state_ in which you want your app to be, without telling it how to get there. The logic that Kubernetes follows internally to change the state of the cluster from where it is to that end state is called _reconciliation_. 74 | 75 | You should always keep the **latest working copy** of your application checked into your source repository (i.e. Github) so that you can always submit it to Kubernetes to get your app into a good state. 76 | 77 | Express your app as a [Helm](https://helm.sh/) chart, so that you are a simple `helm install` away from bringing your app to a good, working state. 78 | 79 | # Ask for the least 80 | 81 | Similar to the [principle of least privilege](https://en.wikipedia.org/wiki/Principle_of_least_privilege), you should always ask Kubernetes for the fewest resources that your app needs to run properly. Leave the rest for Kubernetes to manage for you. 82 | 83 | Here are some examples of resources that you should ask the least from Kubernetes: 84 | 85 | - RBAC permissions 86 | - Containers in a single pod 87 | - CPU shares or memory 88 | - Disk space (i.e. in a `PersistentVolumeClaim`) 89 | 90 | # Build on the shoulders of giants 91 | 92 | The Kubernetes API abstracts away a lot of valuable functionality that is _hard to get right_. This functionality is built by smart people, and tested very thoroughly. Always try to use the Kubernetes API first before you build something from scratch. 93 | 94 | If you can't, look to the cloud native ecosystem. It has a large-and-growing number of high quality software projects that your app can benefit from. 95 | 96 | Finally, if you can't find exactly what you need, pick the next best thing and build atop that (and open source _that_ if you can!) 97 | 98 | We as a community should strive to follow the [don't repeat yourself (DRY)](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself) principle, and this is how we do it. 99 | 100 | 101 | 102 | --------------------------------------------------------------------------------