Diagram Guide

This guide shows you how to create, edit and share diagrams using the Mermaid Javascript library. Mermaid.js allows you to generate diagrams using a simple markdown-like syntax inside Markdown files. You can also use Mermaid to generate .svg or .png image files that you can add to your documentation.

The target audience for this guide is anybody wishing to learn about Mermaid and/or how to create and add diagrams to Kubernetes documentation.

Figure 1 outlines the topics covered in this section.

Figure 1. Topics covered in this section.

All you need to begin working with Mermaid is the following:

• Basic understanding of markdown.
• Using the Mermaid live editor.
• Using Hugo shortcodes.
• Using the Hugo {{< figure >}} shortcode.
• Performing Hugo local previews.
• Familiar with the Contributing new content process.

Why you should use diagrams in documentation

Diagrams improve documentation clarity and comprehension. There are advantages for both the user and the contributor.

The user benefits include:

• Friendly landing spot. A detailed text-only greeting page could intimidate users, in particular, first-time Kubernetes users.
• Faster grasp of concepts. A diagram can help users understand the key points of a complex topic. Your diagram can serve as a visual learning guide to dive into the topic details.
• Better retention. For some, it is easier to recall pictures rather than text.

The contributor benefits include:

• Assist in developing the structure and content of your contribution. For example, you can start with a simple diagram covering the high-level points and then dive into details.
• Expand and grow the user community. Easily consumed documentation augmented with diagrams attracts new users who might previously have been reluctant to engage due to perceived complexities.

You should consider your target audience. In addition to experienced K8s users, you will have many who are new to Kubernetes. Even a simple diagram can assist new users in absorbing Kubernetes concepts. They become emboldened and more confident to further explore Kubernetes and the documentation.

Mermaid

Mermaid is an open source JavaScript library that allows you to create, edit and easily share diagrams using a simple, markdown-like syntax configured inline in Markdown files.

The following lists features of Mermaid:

• Simple code syntax.
• Includes a web-based tool allowing you to code and preview your diagrams.
• Supports multiple formats including flowchart, state and sequence.
• Easy collaboration with colleagues by sharing a per-diagram URL.
• Broad selection of shapes, lines, themes and styling.

The following lists advantages of using Mermaid:

• No need for separate, non-Mermaid diagram tools.
• Adheres to existing PR workflow. You can think of Mermaid code as just Markdown text included in your PR.
• Simple tool builds simple diagrams. You don't want to get bogged down (re)crafting an overly complex and detailed picture. Keep it simple!

Mermaid provides a simple, open and transparent method for the SIG communities to add, edit and collaborate on diagrams for new or existing documentation.

Live editor

The Mermaid live editor is a web-based tool that enables you to create, edit and review diagrams.

The following lists live editor functions:

• Displays Mermaid code and rendered diagram.
• Generates a URL for each saved diagram. The URL is displayed in the URL field of your browser. You can share the URL with colleagues who can access and modify the diagram.
• Option to download .svg or .png files.

Methods for creating diagrams

Figure 2 outlines the three methods to generate and add diagrams.

Figure 2. Methods to create diagrams.

Inline

Figure 3 outlines the steps to follow for adding a diagram using the Inline method.

Figure 3. Inline Method steps.

The following lists the steps you should follow for adding a diagram using the Inline method:

1. Create your diagram using the live editor.
2. Store the diagram URL somewhere for later access.
3. Copy the mermaid code to the location in your .md file where you want the diagram to appear.
4. Add a caption below the diagram using Markdown text.

A Hugo build runs the Mermaid code and turns it into a diagram.

Here is a sample code snippet contained in an .md file:

---
title: My PR
---
Figure 17 shows a simple A to B process.
some markdown text
...
{{< mermaid >}} 
    graph TB
    A --> B
{{< /mermaid >}}

Figure 17. A to B
more text

For more details on diagram captions, see How to use captions.

The following lists advantages of the Inline method:

• Live editor tool.
• Easy to copy Mermaid code to and from the live editor and your .md file.
• No need for separate .svg image file handling.
• Content text, diagram code and diagram caption contained in the same .md file.

You should use the local and Netlify previews to verify the diagram is properly rendered.

Mermaid+SVG

Figure 4 outlines the steps to follow for adding a diagram using the Mermaid+SVG method.

Figure 4. Mermaid+SVG method steps.

The following lists the steps you should follow for adding a diagram using the Mermaid+SVG method:

1. Create your diagram using the live editor.
2. Store the diagram URL somewhere for later access.
3. Generate an .svg image file for the diagram and download it to the appropriate images/ folder.
4. Use the {{< figure >}} shortcode to reference the diagram in the .md file.
5. Add a caption using the {{< figure >}} shortcode's caption parameter.

For example, use the live editor to create a diagram called boxnet. Store the diagram URL somewhere for later access. Generate and download a boxnet.svg file to the appropriate ../images/ folder.

Use the {{< figure >}} shortcode in your PR's .md file to reference the .svg image file and add a caption.

{{< figure src="/static/images/boxnet.svg" alt="Boxnet figure" class="diagram-large" caption="Figure 14. Boxnet caption" >}}

For more details on diagram captions, see How to use captions.

You should add the live editor URL as a comment block in the .svg image file using a text editor. For example, you would include the following at the beginning of the .svg image file:

<!-- To view or edit the mermaid code, use the following URL: -->
<!-- https://mermaid-js.github.io/mermaid-live-editor/edit/#eyJjb ... <remainder of the URL> -->

The following lists advantages of the Mermaid+SVG method:

• Live editor tool.
• Live editor tool supports the most current Mermaid feature set.
• Employ existing K8s/website methods for handling .svg image files.
• Environment doesn't require Mermaid support.

Be sure to check that your diagram renders properly using the local and Netlify previews.

External tool

Figure 5 outlines the steps to follow for adding a diagram using the External Tool method.

First, use your external tool to create the diagram and save it as an .svg or .png image file. After that, use the same steps as the Mermaid+SVG method for adding .svg image files.

Figure 5. External Tool method steps

The following lists the steps you should follow for adding a diagram using the External Tool method:

1. Use your external tool to create a diagram.
2. Save the diagram coordinates for contributor access. For example, your tool may offer a link to the diagram image, or you could place the source code file, such as an .xml file, in a public repository for later contributor access.
3. Generate and save the diagram as an .svg or .png image file. Download this file to the appropriate ../images/ folder.
4. Use the {{< figure >}} shortcode to reference the diagram in the .md file.
5. Add a caption using the {{< figure >}} shortcode's caption parameter.

Here is the {{< figure >}} shortcode for the images/apple.svg diagram:

{{< figure src="/static/images/apple.svg" alt="red-apple-figure" class="diagram-large" caption="Figure 9. A Big Red Apple" >}} 

If your external drawing tool permits:

• You can incorporate multiple .svg or .png logos, icons and images into your diagram. However, make sure you observe copyright and follow the Kubernetes documentation guidelines on the use of third party content.
• You should save the diagram source coordinates for later contributor access. For example, your tool may offer a link to the diagram image, or you could place the source code file, such as an .xml file, somewhere for contributor access.

For more information on K8s and CNCF logos and images, check out CNCF Artwork.

The following lists advantages of the External Tool method:

• Contributor familiarity with external tool.
• Diagrams require more detail than what Mermaid can offer.

Don't forget to check that your diagram renders correctly using the local and Netlify previews.

Examples

This section shows several examples of Mermaid diagrams.

Example 1 - Pod topology spread constraints

Figure 6 shows the diagram appearing in the Pod topology pread constraints page.

Figure 6. Pod Topology Spread Constraints.

Code block:

graph TB
   subgraph "zoneB"
       n3(Node3)
       n4(Node4)
   end
   subgraph "zoneA"
       n1(Node1)
       n2(Node2)
   end
 
   classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
   classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
   classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
   class n1,n2,n3,n4 k8s;
   class zoneA,zoneB cluster;

Example 2 - Ingress

Figure 7 shows the diagram appearing in the What is Ingress page.

Code block:

graph LR;
 client([client])-. Ingress-managed <br> load balancer .->ingress[Ingress];
 ingress-->|routing rule|service[Service];
 subgraph cluster
 ingress;
 service-->pod1[Pod];
 service-->pod2[Pod];
 end
 classDef plain fill:#ddd,stroke:#fff,stroke-width:4px,color:#000;
 classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff;
 classDef cluster fill:#fff,stroke:#bbb,stroke-width:2px,color:#326ce5;
 class ingress,service,pod1,pod2 k8s;
 class client plain;
 class cluster cluster;

Example 3 - K8s system flow

Figure 8 depicts a Mermaid sequence diagram showing the system flow between K8s components to start a container.

Code block:

%%{init:{"theme":"neutral"}}%%
sequenceDiagram
    actor me
    participant apiSrv as control plane<br><br>api-server
    participant etcd as control plane<br><br>etcd datastore
    participant cntrlMgr as control plane<br><br>controller<br>manager
    participant sched as control plane<br><br>scheduler
    participant kubelet as node<br><br>kubelet
    participant container as node<br><br>container<br>runtime
    me->>apiSrv: 1. kubectl create -f pod.yaml
    apiSrv-->>etcd: 2. save new state
    cntrlMgr->>apiSrv: 3. check for changes
    sched->>apiSrv: 4. watch for unassigned pods(s)
    apiSrv->>sched: 5. notify about pod w nodename=" "
    sched->>apiSrv: 6. assign pod to node
    apiSrv-->>etcd: 7. save new state
    kubelet->>apiSrv: 8. look for newly assigned pod(s)
    apiSrv->>kubelet: 9. bind pod to node
    kubelet->>container: 10. start container
    kubelet->>apiSrv: 11. update pod status
    apiSrv-->>etcd: 12. save new state

How to style diagrams

You can style one or more diagram elements using well-known CSS nomenclature. You accomplish this using two types of statements in the Mermaid code.

• classDef defines a class of style attributes.
• class defines one or more elements to apply the class to.

In the code for figure 7, you can see examples of both.

classDef k8s fill:#326ce5,stroke:#fff,stroke-width:4px,color:#fff; // defines style for the k8s class
class ingress,service,pod1,pod2 k8s; // k8s class is applied to elements ingress, service, pod1 and pod2.

You can include one or multiple classDef and class statements in your diagram. You can also use the official K8s #326ce5 hex color code for K8s components in your diagram.

For more information on styling and classes, see Mermaid Styling and classes docs.

How to use captions

A caption is a brief description of a diagram. A title or a short description of the diagram are examples of captions. Captions aren't meant to replace explanatory text you have in your documentation. Rather, they serve as a "context link" between that text and your diagram.

The combination of some text and a diagram tied together with a caption help provide a concise representation of the information you wish to convey to the user.

Without captions, you are asking the user to scan the text above or below the diagram to figure out a meaning. This can be frustrating for the user.

Figure 9 lays out the three components for proper captioning: diagram, diagram caption and the diagram referral.

Diagram

The Mermaid+SVG and External Tool methods generate .svg image files.

Here is the {{< figure >}} shortcode for the diagram defined in an .svg image file saved to /images/docs/components-of-kubernetes.svg:

{{< figure src="/images/docs/components-of-kubernetes.svg" alt="Kubernetes pod running inside a cluster" class="diagram-large" caption="Figure 4. Kubernetes Architecture Components >}}

You should pass the src, alt, class and caption values into the {{< figure >}} shortcode. You can adjust the size of the diagram using diagram-large, diagram-medium and diagram-small classes.

See Methods for creating diagrams for more information on the different methods for creating diagrams.

Diagram Caption

Next, add a diagram caption.

If you define your diagram in an .svg image file, then you should use the {{< figure >}} shortcode's caption parameter.

{{< figure src="/images/docs/components-of-kubernetes.svg" alt="Kubernetes pod running inside a cluster" class="diagram-large" caption="Figure 4. Kubernetes Architecture Components" >}}

If you define your diagram using inline Mermaid code, then you should use Markdown text.

Figure 4. Kubernetes Architecture Components

The following lists several items to consider when adding diagram captions:

• Use the {{< figure >}} shortcode to add a diagram caption for Mermaid+SVG and External Tool diagrams.
• Use simple Markdown text to add a diagram caption for the Inline method.
• Prepend your diagram caption with Figure NUMBER.. You must use Figure and the number must be unique for each diagram in your documentation page. Add a period after the number.
• Add your diagram caption text after the Figure NUMBER. on the same line. You must puncuate the caption with a period. Keep the caption text short.
• Position your diagram caption BELOW your diagram.

Diagram Referral

Finally, you can add a diagram referral. This is used inside your text and should precede the diagram itself. It allows a user to connect your text with the associated diagram. The Figure NUMBER in your referral and caption must match.

You should avoid using spatial references such as ..the image below.. or ..the following figure ..

Here is an example of a diagram referral:

Figure 10 depicts the components of the Kubernetes architecture.
The control plane ...

Diagram referrals are optional and there are cases where they might not be suitable. If you are not sure, add a diagram referral to your text to see if it looks and sounds okay. When in doubt, use a diagram referral.

Complete picture

Figure 10 shows the Kubernetes Architecture diagram that includes the diagram, diagram caption and diagram referral. The {{< figure >}} shortcode renders the diagram, adds the caption and includes the optional link parameter so you can hyperlink the diagram. The diagram referral is contained in this paragraph.

Here is the {{< figure >}} shortcode for this diagram:

{{< figure src="/images/docs/components-of-kubernetes.svg" alt="Kubernetes pod running inside a cluster" class="diagram-large" caption="Figure 10. Kubernetes Architecture." link="https://kubernetes.io/docs/concepts/overview/components/" >}}

Tips

• Always use the live editor to create/edit your diagram.

• Always use Hugo local and Netlify previews to check out how the diagram appears in the documentation.

• Include diagram source pointers such as a URL, source code location, or indicate the code is self-documenting.

• Always use diagram captions.

• Very helpful to include the diagram .svg or .png image and/or Mermaid source code in issues and PRs.

• With the Mermaid+SVG and External Tool methods, use .svg image files because they stay sharp when you zoom in on the diagram.

• Best practice for .svg files is to load it into an SVG editing tool and use the "Convert text to paths" function. This ensures that the diagram renders the same on all systems, regardless of font availability and font rendering support.

• No Mermaid support for additional icons or artwork.

• Hugo Mermaid shortcodes don't work in the live editor.

• Any time you modify a diagram in the live editor, you must save it to generate a new URL for the diagram.

• Click on the diagrams in this section to view the code and diagram rendering in the live editor.

• Look over the source code of this page, diagram-guide.md, for more examples.

• Check out the Mermaid docs for explanations and examples.

Most important, Keep Diagrams Simple. This will save time for you and fellow contributors, and allow for easier reading by new and experienced users.