Update README.md with Helm install instructions

README.md

@@ -6,7 +6,9 @@ the current IP in an AWS route 53 record.
 
 ## Usage
 
-```
+### Docker
+
+```shell
 docker run -d \
     --name update-route53 \
     -e AWS_ACCESS_KEY_ID=<your access key id> \
@@ -16,3 +18,106 @@ docker run -d \
     -e DNS_NAME=myhost.domain.com \
     ghcr.io/jpflouret/update-route53:latest
 ```
+
+### Kubernetes Helm Chart
+
+Add the chart repo:
+```shell
+helm repo add update-route53 https://jpflouret.github.io/update-route53/
+helm repo update
+```
+
+Create `my-values.yaml` configuration file with default values:
+```shell
+helm show values update-route53/update-route53 > my-values.yaml
+```
+
+Edit the `my-values.yaml` file and set the values as required:
+| Key            | Required? | Description                                                                    | Default                                                    |
+| -------------- | --------- | ------------------------------------------------------------------------------ | -----------------------------------------------------------|
+| `dnsName`      | Yes       | Host name to update                                                            | `""`                                                       |
+| `hostedZoneId` | Yes       | Hosted zone id to update                                                       | `""`                                                       |
+| `dnsTTL`       | No        | TTL for the DNS record                                                         | `300`<br>(Default in executable)                           |
+| `chechIPURL`   | No        | URL to check the public IP address                                             | `http://checkip.amazonaws.com/`<br>(Default in executable) |
+| `sleepPeriod`  | No        | Sleep period between IP address checks                                         | `5m`                                                       |
+| `tolerations`  | No        | List of kubernetes node taints that are tolerated by the `update-route53` pods | Empty                                                      |
+| `nodeSelector` | No        | List of labels used to select which nodes can run `update-route53` pods        | Empty                                                      |
+
+Recommended tolerations to allow execution in control plane nodes:
+```yaml
+tolerations:
+  - key: node-role.kubernetes.io/control-plane
+    operator: Exists
+    effect: NoSchedule
+  - key: node-role.kubernetes.io/master
+    operator: Exists
+    effect: NoSchedule
+```
+
+#### AWS Credentials
+The AWS credentials are supplied to the pod with a kubernetes secret.
+The secret should contain the following keys:
+- `AWS_ACCESS_KEY_ID`
+- `AWS_SECRET_ACCESS_KEY`
+- `AWS_DEFAULT_REGION`
+
+You can create the secret using `kubectl`:
+```shell
+kubectl kubectl create secret generic aws-credentials \
+  --namespace <namespace>
+  --from-literal=AWS_ACCESS_KEY_ID=<access key id> \
+  --from-literal=AWS_SECRET_ACCESS_KEY=<secret access key> \
+  --from-literal=AWS_DEFAULT_REGION=<aws region>
+```
+
+When installing the chart, set `secret.existingSecret` to the name of
+the secret created above (`aws-credentials` in this example):
+```shell
+helm install \
+  my-update-route53 \
+  update-route53/update-route53 \
+  --namespace <namespace> \
+  --values my-values.yaml \
+  --set=secret.existingSecret=aws-credentials
+```
+
+Alternatively, the secret can be created at chart installation time using
+the following configuration values:
+| Key                      | Required?                               | Description                                                  | Default                                   |
+| ------------------------ | ----------------------------------------| ------------------------------------------------------------ | ------------------------------------------|
+| `secret.create`          | No                                      | Set to `true` to create a secret as part of the Helm release | `false`                                   |
+| `secret.accessKeyId`     | Yes if `secret.create` is set to `true` | AWS Access Key ID to use when creating the secret            | `""`                                      |
+| `secret.secretAccessKey` | Yes if `secret.create` is set to `true` | AWS Secret Access Key to use when creating the secret        | `""`                                      |
+| `secret.awsRegion`       | No                                      | AWS Region to use when creating the secret                   | `"us-west-2"`<br>(Defaults in executable) |
+
+#### Metrics
+The pod exposes prometheus metrics on port `8080` on the `/metrics` path.
+You can create a service and configure prometheus to scrape the metrics
+endpoint automatically using service annotations.
+
+Metrics configuration values:
+| Key                   | Required? | Description                                | Default     |
+| --------------------- | --------- | ------------------------------------------ | ----------- |
+| `service.create`      | No        | Crete a service for the metrics endpoint.  | `false`     |
+| `service.type`        | No        | Type of service metrics enpoint.           | `ClusterIP` |
+| `service.annotations` | No        | Annotations to add to the metrics endpont. | Empty       |
+
+You can configure prometheus to scrape the service endpoint automatically by
+adding the following annotations to the service (in `my-values.yaml`):
+```yaml
+service:
+  create: true
+  annotations:
+    prometheus.io/scrape: "true"
+    prometheus.io/path: /metrics
+    prometheus.io/port: "8080"
+```
+
+#### Service Account
+If you need to, you can create a kubernetes service account for use with
+`update-route53` pods using the following configuration variables:
+
+| Key                     | Required? | Description                                          | Default                                 |
+| ----------------------- | --------- | ---------------------------------------------------- | --------------------------------------- |
+| `serviceAccount.create` | No        | Create a kubernetes service account for the release. | `false`                                 |
+| `serviceAccount.name`   | No        | Name of the service account to use                   | Defaults to the full helm release name. |