025 external DNS

src/025_external_dns.md

@@ -0,0 +1,27 @@
+# ExternalDNS
+
+The workflow for accessing our `LoadBalancer` services ain't great.
+
+If we deploy a new application, we need to run `kubectl -n <namespace> get svc` and read through a list to determine the IP address on which it's exposed. And that's not going to be stable; there's nothing at all guaranteeing that Argo CD will always be available at `http://10.4.11.1`.
+
+Enter [ExternalDNS](https://github.com/kubernetes-sigs/external-dns). The idea is that we annotate our services with `external-dns.alpha.kubernetes.io/hostname: "argocd.my-cluster.my-domain.com"` and a DNS record will be created pointing to the actual IP address of the `LoadBalancer` service.
+
+This is comparatively straightforward to configure if you host your DNS in one of the supported services. I host mine via AWS Route53, which is supported.
+
+The complication is that we don't yet have a great way of managing secrets, so there's a manual step here that I find unpleasant, but we'll cross that bridge when we get to it.
+
+Because of work we've done previously with Argo CD, we can just create [a new repository](https://github.com/goldentooth/external-dns) to deploy ExternalDNS within our cluster.
+
+This has the following manifests:
+
+- **Deployment**: The deployment has several interesting features:
+  - This is where the `--provider` (`aws`) is configured.
+  - We specify `--source`s (in our case `service`).
+  - A `--domain-filter` allows us to use different configurations for different domain names.
+  - A `--txt-owner-id` allows us to map from a record back to the application that created it.
+  - Mounts a secret  as AWS credentials (I used static credentials for the time being) so ExternalDNS can make the changes in Route53.
+- **ServiceAccount**: Just adds a service account for ExternalDNS.
+- **ClusterRole**: Describes an ability to observe changes in services.
+- **ClusterRoleBinding**: Binds the above cluster role and ExternalDNS.
+
+A few minutes after pushing changes to the repository, we can reach Argo CD via https://argocd.goldentooth.hellholt.net/.

src/SUMMARY.md

@@ -24,3 +24,4 @@
 - [Testing MetalLB](./022_testing_metallb.md)
 - [Refactoring Argo CD](./023_refactoring_argocd.md)
 - [Giving Argo CD a Load Balancer](./024_argocd_load_balancer.md)
+- [ExternalDNS](./025_external_dns.md)