> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Transformers Demo
> This guide demonstrates using transformation techniques with Kustomize, including managing Kubernetes configurations and applying common labels, namespaces, and image transformations.
In this guide, we demonstrate how to use common transformation techniques with Kustomize, including the image transformer. We also review the directory structure used in this demonstration to help you manage and organize Kubernetes configurations efficiently.
## Directory Structure Overview
Assume you have a directory named "K8s" containing two subdirectories: "API" and "database".
* In the **API** directory, you will find:
* API deployment YAML file (e.g., `api-depl.yaml`)
* API service YAML file (e.g., `api-service.yaml`)
* `kustomization.yaml`
* In the **database** directory, you will find:
* Database deployment YAML file (e.g., `db-depl.yaml`)
* Database service YAML file (e.g., `db-service.yaml`)
* Config YAML file (e.g., `db-config.yaml`)
* `kustomization.yaml`
Each subdirectory’s `kustomization.yaml` is configured to import and manage all resources within that directory. For instance, the **API** directory’s `kustomization.yaml` might look like this:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api-depl.yaml
- api-service.yaml
```
And the **database** directory’s `kustomization.yaml` imports the database configurations:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- db-config.yaml
- db-depl.yaml
- db-service.yaml
```
At the root level, the `kustomization.yaml` aggregates the API and database configurations:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api/
- db/
```
## Applying a Common Label
To add a common label to all resources, modify the root `kustomization.yaml` file. For example, to add the label `department: engineering` to every resource:
1. Open the root `kustomization.yaml`.
2. Add the common label configuration.
3. Save the file and run the Kustomize build command.
When you run:
```bash theme={null}
kustomize build k8s/
```
the output will include all the resources with the label `department: engineering`. For example, a ConfigMap might appear as follows:
```yaml theme={null}
apiVersion: v1
data:
password: example
username: root
kind: ConfigMap
metadata:
labels:
department: engineering
name: db-credentials
---
apiVersion: v1
kind: Service
metadata:
labels:
department: engineering
name: api-service
spec:
ports:
- port: 80
protocol: TCP
targetPort: 3000
```
All resources in both the API and database directories now include the `department: engineering` label.
## Label Application in Subdirectories
When you add a common label within a subdirectory's `kustomization.yaml` rather than in the root file, the label will only affect resources within that subdirectory. For example, if you apply a label in the API directory like so:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api-depl.yaml
- api-service.yaml
commonLabels:
feature: api
```
the `feature: api` label is applied only to the resources listed in that file. This means that the API service will have both the root label (`department: engineering`) and the subdirectory-specific label (`feature: api`), while resources in the database directory will only have the global label.
A snippet of the resulting output could look like:
```yaml theme={null}
apiVersion: v1
data:
password: example
username: root
kind: ConfigMap
metadata:
labels:
department: engineering
name: db-credentials
---
apiVersion: v1
kind: Service
metadata:
labels:
department: engineering
feature: api
name: api-service
spec:
ports:
- port: 80
protocol: TCP
targetPort: 3000
```
To differentiate between API and database resources further, you can add common labels specific to the database environment in the database directory’s `kustomization.yaml`. For example:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- db-config.yaml
- db-depl.yaml
- db-service.yaml
commonLabels:
feature: db
```
After building the configuration, database resources will include:
```yaml theme={null}
metadata:
labels:
department: engineering
feature: db
```
## Setting a Specific Namespace
To place all resources into a specific namespace, such as a debugging environment, add the `namespace` field to your root `kustomization.yaml`. For example:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api/
- db/
commonLabels:
department: engineering
namespace: debugging
```
After running the build, all resources from both API and database directories will be assigned the namespace `debugging`.
## Adding Name Prefixes and Suffixes
If you want every object name to have a common prefix (e.g., "KodeKloud-") with folder-specific suffixes (like `-web` for API resources and `-storage` for database resources), follow these steps:
### Adding a Global Name Prefix
Edit the root `kustomization.yaml` to include the prefix:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api/
- db/
commonLabels:
department: engineering
namespace: debugging
namePrefix: KodeKloud-
```
After this change, the API deployment name might appear as `KodeKloud-api-deployment` (with an additional suffix appended later).
### Adding Folder-Specific Name Suffixes
For the API subdirectory, add a name suffix in its `kustomization.yaml`:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- api-depl.yaml
- api-service.yaml
commonLabels:
feature: api
nameSuffix: -web
```
For the database subdirectory, add a different name suffix:
```yaml theme={null}
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- db-config.yaml
- db-depl.yaml
- db-service.yaml
commonLabels:
feature: db
nameSuffix: -storage
```
After rebuilding, you will see that API resource names end with `-web` while database resource names end with `-storage`, all prefixed by "KodeKloud-". For example, the API service might be named:
```yaml theme={null}
name: KodeKloud-api-deployment-web
```
and the database deployment might be:
```yaml theme={null}
name: KodeKloud-db-deployment-storage
```
## Adding a Common Annotation
To apply a common annotation across every resource, add the following to your root `kustomization.yaml`:
```yaml theme={null}
commonAnnotations:
logging: verbose
```
After rebuilding, every resource will include the annotation `logging: verbose`.
## Image Transformation
Finally, let’s look at how to update container images using the image transformer. Consider a scenario where a database deployment is set to use the Mongo image, but you want to replace it with Postgres using a specific tag.
In the database directory’s `kustomization.yaml` (or in another appropriate configuration file), add an image transformer configuration like this:
```yaml theme={null}
images:
- name: mongo
newName: postgres
newTag: "4.2"
```
This configuration instructs Kustomize to search for any container image named "mongo" and update it to "postgres:4.2". Note that only the image is updated; the container’s name remains unchanged.
Ensure you enclose the new tag in quotes to avoid type conversion issues (e.g., `newTag: "4.2"`). This prevents errors such as:
Error: accumulating resources: ... json: cannot unmarshal number into Go struct field Image.images.newTag of type string
After applying this transformer and running:
```bash theme={null}
kustomize build k8s/
```
the database deployment’s container image should update to:
```yaml theme={null}
image: postgres:4.2
```
while all other image configurations remain untouched.
## Wrapping Up
This guide demonstrated how to:
* Organize Kubernetes configuration files into modular directories.
* Apply common labels, name prefixes, and suffixes globally or specifically in each subdirectory.
* Configure a namespace and common annotations.
* Use an image transformer to update container images seamlessly.
In the next section, try the lab exercises to gain hands-on experience with customizing Kustomize configurations and transformers.
Happy customizing!