Introduction

It has become the standard API for building cloud native applications. It provides the software needed for build and deploy, reliable, scalable distributed systems.

Distributed systems: Most services nowadays are delivered via the network, they have different moving parts in different machines talking to each other over the network via APIs.

Reliable: Since we rely a lot on these distributed systems, they cannot fail, even if some part of them crashes, they need to be kept up and running, and be fault-tolerant

Availability: They must still be available during maintenance, updates, software rollouts and so on.

Scalable: We live in a highly connected society, so these systems need to be able to grow their capacity without radical redesign of the distributed systems.

Most of the reasons people come to use containers and container orchestration like k8s, can be boil down to 5 things: velocity, scaling, abstracting your infra, efficiency, cloud native ecosystem

Development Velocity

Today software is delivered via de network more quickly than ever, but velocity is not just a matter of raw speed, people are more interested in a highly reliable service, all users expect constant uptime, even as the software is being updated.

Velocity is measures in term of the number of things you can ship while maintaining a highly available service.

k8s give you the tools to to do this, the core concepts to enable this are:

• Immutability

  Software used to be mutable (imperative), you installed vim using dnf and then one day you would do dnf update and it would add modifications on top of the binary that you already have for vim. This is what we call mutable software.

  On the other hand, immutable software, you would not add on top of the previous release, you would build the image from zero. Which is how containers work. Basically when you want to update something in a container, you do not go inside it and do dnf update vim you create a new image with the version of vim you want, destroy the old one, and create a container with the new one.

  This makes rollbacks way easier, and it keeps tracks of what changed from version to version.

• Declarative Configuration

  This is an extension of immutability but for the configuration. It basically means that you have a file where you defined the ideal state of your system. The idea of storing this files in source control is often called “infrastructure as code”.

  The combination of declarative state stored in a version control system and the ability of k8s to make it match the state makes rollback super easy.

• Self-Healing Systems

  K8s will continuously take action to make sure the state on the declarative configuration is met. Say it has declared 3 replicas, then if you go and create one extra, it will kill it, and if you were to destroy one, it would create it.

  This means that k8s will not only init your system but will guard it against any failures that might destabilize it.

Scaling Your Service and Your Teams

K8s is great for scaling because of its decoupled architecture.

Decoupling

In a decoupled architecture each components is separated from each other by defined APIs and service loads

This basically means that we can isolate each service.

• The API provide a buffer between implementer and consumer.
• Load balancing provide a buffer between running instances of each service.

When we decouple the services, it makes it easier to scale, since each small team can focus on a single microservice

Scaling for Applications and Clusters

Since your app is deployed in containers, which are immutable, and th configuration o is also declarative, scaling simply becomes a matter of changing a number in a configuration file. Or you can even tell k8s to do that for you.

Of course k8s will be limited to the resources you have, it will not create a physical computer on demand. But k8s makes it easier to scale the cluster itself as well.

Since a set of machines in a cluster are identical and the apps are decoupled from the specifics of the machine by containers, scaling a cluster is just a matter of provisioning the system and joining it to a cluster.

K8s can also come in handy when trying to forecast costs on growth and scaling. Basically, if you have different apps that need to scale from many teams, you can aggregate them all in a single k8s, and try to forecast the usage of the 3 apps together.

Scaling Development Teams

Teams are ideal when using the two-pizza team when (6 to 8 people), larger teams tend to have issues of hierarchy, poor visibility, infighting and so on.

K8s can help with that, since you can have multiple small teams working on different microservices and aggregate them all into a single k8s cluster.

K8s has different abstractions that make it easier to build decoupled microservices.

• pods: are groups of containers, can contain images developed by different teams into a single deployable unit.
• k8s services: provide load balancing, naming and discovery to isolate the microservices.
• namespaces: provide isolation and access control, so that each microservice can control the degree to which other services interact with it.
• ingress: easy to use front end that can combine microservices into a single API.

Separation of Concerns for Consistency and Scaling

K8s leads to greater consistency for the lower levels of the infrastructure. Basically the devs need to only worry about their app meeting the SLA (service level agreements) while the orchestration admin only need to worry about reaching the SLA from their side.

Abstracting You Infrastructure

When you build your app in terms of containers and deploy it via k8s APIs, you make moving your app between environments super easy. It is simply a question of sending the declarative config to a new cluster.

K8s make building deploying and managing your app truly portable across a wide variety of environments

Efficiency

Efficiency is measured by the ratio of the useful work performed by a machine.

K8s enables efficiency in multiple ways. Since developers do not need to use a whole machine for himself/herself, but rather one container, multiple users can share the same baremetal. Meaning less idle CPUs.

Cloud Native Ecosystem

K8s is open source and has a huge community building a thousand things on top of it. You can check the maturity of different projects in Cloud Native Computing Foundation. The maturities are sandbox incubating and graduated, going from less mature to most mature.

Summary

Fundamentally k8s was design to give developers more velocity efficiency and agility. Now that we have seen why to use it, lets see how to use it.