<h1 id="kubernetes-objects">Kubernetes Objects<a aria-hidden="true" class="anchor-heading icon-link" href="#kubernetes-objects"></a></h1>
An object is a persistent entity in the Kubernetes system. Each object represents a part of the state of our cluster, and all of them together represent the whole desired state.
Objects can describe:
<ul>
<li>What containerized applications are running (and on which <a href="/notes/iuja3tlxkdniv862fq9h1v4">nodes</a>)</li>
<li>The resources available to those applications</li>
<li>The policies around how those applications behave (e.g. restart policies, upgrades, <a href="/notes/mh3gii3m3gs5etkb2alcifl">fault tolerance</a> etc.)</li>
</ul>
An object is a "record of intent"— it is our way of declaring the cluster's desired state.
<ul>
<li>once you create the object, the Kubernetes system will constantly work to ensure that object exists.</li>
</ul>
To create, read or modify an object, we interact with the <a href="/notes/hecaydk40a6wqiprau7l8qz">Kubernetes API</a>.
<ul>
<li>If we are using <a href="/notes/nhxmrkFjzHtZZmOBkWfhh">Kubectl</a>, calls to the API will be made for us.</li>
</ul>
Almost every object should take this shape:
<pre class="language-js"><code class="language-js">{
 spec: {
 // desired state
 },
 status: // current state of the object, managed by the control plane
}
</code></pre>
Even though we can create services by running <code>kubectl expose</code>, we should typically follow a documented approach by using YAML files.
<h2 id="fields">Fields<a aria-hidden="true" class="anchor-heading icon-link" href="#fields"></a></h2>
<h3 id="selector"><code>selector</code><a aria-hidden="true" class="anchor-heading icon-link" href="#selector"></a></h3>
<pre class="language-yml"><code class="language-yml">selector:
 matchLabels:
 app: hellok8s
</code></pre>
What we are doing in this field is telling Kubernetes that this object is managing all the pods that have a label called <code>app</code> with the value <code>hellok8s</code>. This is what links our object to pods.
<ul>
<li>Labels are simply key-value pairs that you define for your pods, and that’s what is used to find all the pods that a Deployment needs to look after.</li>
</ul>
<hr>
Children
<ol>
<li><a href="/notes/q1zb6dpa8v7var4rxbrctwn">Configmap</a></li>
<li><a href="/notes/ZK0P0va9kOJGsM9X7X2Td">Deployment</a></li>
<li><a href="/notes/cnkzosrbq8pdbru80p9c7h0">HorizontalPodAutoscaler</a></li>
<li><a href="/notes/4b0Xz0VUtXbFaFl1Pri9E">Kubernetes Ingress</a></li>
<li><a href="/notes/a9WtJDyCZ4NvEaAZ4p3bd">Kubernetes Pod</a></li>
<li><a href="/notes/ryBzcGWSKyybRXnyKxteV">Kubernetes Service</a></li>
<li><a href="/notes/lmBa9fwj8huQ5pCXAyQNq">Namespace</a></li>
<li><a href="/notes/w9bmyk2szy9zwwxz1ccttxt">PodDisruptionBudget</a></li>
<li><a href="/notes/dujlr4c5st1zdhogi2h7pos">Service Accou</a></li>
<li><a href="/notes/Yo1A54kOWjZXTtNcEIuP5">Volume</a></li>
</ol>
<hr>
Backlinks
<ul>
<li><a href="/notes/nhxmrkFjzHtZZmOBkWfhh">Kubectl</a></li>
<li><a href="/notes/hecaydk40a6wqiprau7l8qz">API Server</a></li>
</ul>

Kubernetes Objects

tech

This Dendron vault of tech knowledge is organized according to domains and their sub-domains, along with specific implementation of those domains.

For instance, Git itself is a domain. Sub-domains of Git would include topics like `commit`,
`tags`, `reflog` etc., while implementations of each of those could be `cli`, `strat`
(strategies), `inner` (inner workings), and so on.

The goal of the wiki is to present data in a manner that is from the perspective
of a querying user. Here, a user is a programmer wanting to get key information
from a specific domain. For instance, if a user wants to use postgres functions
and hasn't done them in a while, they should be able to query
`postgres.functions` to see basic implementations, as well as common patterns
that have been employed in the past.

This wiki has been written with myself in mind. While learning each of these
domains, I have been sensitive to the "aha" moments and have noted down my
insights as they arose. I have refrained from capturing information that I
considered obvious or otherwise non-beneficial to my own understanding.

As a result, I have allowed myself to use potentially arcane concepts to help
explain others. For example, in my note on [[unit testing|testing.method.unit]],
I have made reference to the [[microservices|general.arch.microservice]] note.
The ability to analogize between different concepts captured in different notes
allows an opportunity to build strong generalized understandings. Given that
you'd have to understand microservices to be able to draw that same parallel
that I've already drawn, these links won't work for everyone. Since these notes
are written for myself, I have been fine with taking these liberties and leaning
on them heavily.

What I hope to gain from this wiki is the ability to step away from any
given domain for a long period of time, and be able to be passably useful for
whatever my goals are within a short period of time. Of course this is all
vague sounding, and really depends on the domain along with the ends I am
trying to reach.

To achieve this, the system should be steadfast to:
- be able to put information in relatively easily, without too much thought
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	- Some concepts might realistically belong to multiple domains. For instance, the concept of *access modifiers* can be found in both `C#` and `Typescript`. Therefore, this note should be abstracted to a common place, such as [[OOP|paradigm.oop]].

This Dendron notebook is the sister vault to the general [Second Brain](https://tech.kyletycholiz.com).

## Tags
Throughout the garden, I have made use of tags, which give semantic meaning to the pieces of information.

- `ex.` - Denotes an *example* of the preceding piece of information
- `spec:` - Specifies that the preceding information has some degree of *speculation* to it, and may not be 100% factual. Ideally this gets clarified over time as my understanding develops. I try to go back after I have better understood the topic and clear out the notes of `spec:` tags
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- `mn:` - Denotes a *mnemonic*
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## Resources
### UE (Unexamined) Resources
Often, I come across sources of information that I believe to be high-quality. They may be recommendations or found in some other way. No matter their origin, I may be in a position where I don't have the time to fully examine them (and properly extract notes), or I may not require the information at that moment in time. In cases like these, I will add reference to a section of the note called **UE Resources**. The idea is that in the future when I am ready to examine them, I have a list of resources that I can start with. This is an alternative strategy to compiling browser bookmarks, which I've found can quickly become untenable.

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### Resources
This heading is for inexhaustible resources. 
- A prime example would be a quality website that continually posts articles.  - Another example would be a tool, such as software that measures frequencies in a room to help acoustically treat it.
