# Amazon EKS + DocumentDB (Terraform)

Terraform stack that creates a **basic Kubernetes cluster (EKS) and a managed
MongoDB-compatible database (Amazon DocumentDB) on AWS**, wired together so
Kerberos Hub can be installed on it straight away.

It is primarily meant as a **reproducible test environment** for the DocumentDB
support in the [`hub` helm chart](https://github.com/kerberos-io/helm-charts),
in particular the `mongodb.tls.*` values that mount the Amazon RDS certificate
authority bundle. It is deliberately small and cheap, not a hardened production
landing zone.

## What it creates

```mermaid
flowchart LR
    subgraph VPC["VPC (10.20.0.0/16)"]
        subgraph Public["Public subnets"]
            NAT[NAT gateway]
            LB[Load balancers]
        end
        subgraph Private["Private subnets"]
            NODES[EKS managed node group]
            DOCDB[(DocumentDB cluster<br/>TLS enforced)]
        end
    end
    EKSCP[EKS control plane] --- NODES
    NODES -- "27017 / TLS" --> DOCDB
    NODES --> NAT
```

| Component | Details |
| --------- | ------- |
| VPC | Public + private subnets across 3 availability zones, internet gateway, NAT gateway |
| EKS | Managed control plane, one managed node group, `coredns`, `kube-proxy`, `vpc-cni`, `eks-pod-identity-agent` and `aws-ebs-csi-driver` add-ons (IRSA role included) |
| DocumentDB | Cluster + instances in the private subnets, encryption **at rest** (KMS) and **in transit** (`tls=enabled`), subnet group, cluster parameter group |
| Security | A dedicated security group that only allows port `27017` from the EKS worker node security group (plus any extra CIDRs you pass in) |

> [!IMPORTANT]
> DocumentDB has **no public endpoint**. It can only be reached from inside the
> VPC, which is why the workloads that talk to it must run on this cluster (or
> you must tunnel through a bastion host / VPN).

> [!WARNING]
> This stack costs money while it exists (EKS control plane, NAT gateway, EC2
> nodes, DocumentDB instances and storage). Run `terraform destroy` when you are
> done.

## Prerequisites

- [Terraform](https://developer.hashicorp.com/terraform/downloads) >= 1.5
- [AWS CLI](https://docs.aws.amazon.com/cli/latest/userguide/getting-started-install.html) v2, authenticated with permissions to create VPC, EKS, IAM and DocumentDB resources
- `kubectl` and `helm`

## Usage

```bash
cd deployment/modules/amazon-eks-documentdb

cp terraform.tfvars.example terraform.tfvars
$EDITOR terraform.tfvars

terraform init
terraform plan
terraform apply
```

Creating the cluster and the database takes a while (EKS and DocumentDB are
both slow to provision).

### Replacing the VPC

AWS cannot move a DocumentDB subnet group or cluster between VPCs. The subnet
group name therefore includes the VPC ID, allowing Terraform to create a new
group and replace the cluster when the VPC changes instead of attempting an
unsupported in-place subnet update.

Discard any saved plan created before a VPC replacement or configuration
change, then create and apply a fresh one:

```bash
rm -f tfplan
terraform plan -out=tfplan
terraform apply tfplan
```

> [!WARNING]
> Replacing the VPC also replaces the DocumentDB cluster. If it contains data,
> create and verify a snapshot before applying the plan; a final snapshot
> preserves the old data but is not restored into the replacement cluster
> automatically.

State is kept locally by default. For anything shared, add a backend, for
example:

```hcl
terraform {
  backend "s3" {
    bucket = "my-terraform-state"
    key    = "kerberos-hub/eks-documentdb.tfstate"
    region = "eu-west-1"
  }
}
```

### Connect kubectl

```bash
$(terraform output -raw update_kubeconfig_command)
kubectl get nodes
```

## Installing Kerberos Hub against DocumentDB

### 1. Create the certificate authority secret

DocumentDB presents a certificate signed by the Amazon RDS certificate
authority, so every client needs the bundle:

```bash
kubectl create namespace kerberos-hub

curl -O https://truststore.pki.rds.amazonaws.com/global/global-bundle.pem
kubectl create secret generic mongodb-ca \
  --from-file=global-bundle.pem \
  -n kerberos-hub
```

### 2. Generate the values

```bash
terraform output -raw hub_values_snippet > hub-documentdb-values.yaml
```

Which produces something like:

```yaml
mongodb:
  flavor: "documentdb"
  retryWrites: "false"
  uri: "mongodb://kerberos:...@kerberos-hub-docdb.cluster-xxxx.eu-west-1.docdb.amazonaws.com:27017/?replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false"
  adminDatabase: "admin"
  authenticationMechanism: "SCRAM-SHA-1"
  tls:
    enabled: true
    existingSecret: "mongodb-ca"
    caFileName: "global-bundle.pem"
    mountPath: "/certs"
```

The chart mounts the bundle into every workload that talks to MongoDB, appends
`tls=true&tlsCAFile=/certs/global-bundle.pem` to the URI, and exposes
`MONGODB_TLS`, `MONGODB_TLS_CA_FILE` and `MONGODB_TLS_INSECURE_SKIP_VERIFY`
through the `mongodb-config` ConfigMap.

> [!NOTE]
> With DocumentDB you must configure the database through `mongodb.uri`, not
> through `mongodb.host` / `mongodb.username` / `mongodb.password`, so that the
> TLS parameters end up in the connection string that every service uses.

### 3. Install the chart

```bash
helm repo add kerberos https://charts.kerberos.io
helm install hub kerberos/hub \
  --version 0.127.0 \
  -n kerberos-hub \
  -f your-hub-values.yaml \
  -f hub-documentdb-values.yaml
```

The `hub_values_snippet` output contains credentials, so treat the generated
file as a secret and do not commit it.

### 4. Verify

```bash
kubectl logs -n kerberos-hub deploy/hub-api | head -50
kubectl exec -n kerberos-hub deploy/hub-api -- ls -l /certs
```

A one-off connectivity check from inside the cluster:

```bash
kubectl run mongosh --rm -it --restart=Never -n kerberos-hub \
  --image=mongodb/mongodb-community-server:7.0-ubi8 \
  --overrides='{"spec":{"volumes":[{"name":"ca","secret":{"secretName":"mongodb-ca"}}],"containers":[{"name":"mongosh","image":"mongodb/mongodb-community-server:7.0-ubi8","stdin":true,"tty":true,"command":["mongosh"],"args":["'"$(terraform output -raw mongodb_uri)"'&tls=true&tlsCAFile=/certs/global-bundle.pem"],"volumeMounts":[{"name":"ca","mountPath":"/certs"}]}]}}'
```

### 5. Import the example Hub data

This module has a separate DocumentDB import under [`database-import`](database-import).
It uses the chart-managed `mongodb-config`, mounts `mongodb-ca`, forces TLS with
the Amazon RDS CA bundle, and refuses to run unless the backend flavor is
`documentdb` with retryable writes disabled. Install Hub chart `0.127.0` or
newer before running it.

Run it after installing Hub:

```bash
./database-import/run.sh
```

The import is idempotent: it upserts two example users, one subscription and
five settings documents using fixed IDs, then verifies those records. It can be
rerun after deleting or replacing the DocumentDB cluster.

| Account | Password | Role |
| ------- | -------- | ---- |
| `example-user` | `example-password` | Hub owner |
| `example-application` | `example-password` | Admin application |

These are public example credentials. Do not use this seed data in a production
deployment.

## Persistent volumes

The EBS CSI driver is installed, but EKS ships `gp2` as the default storage
class. To use `gp3` instead:

```bash
kubectl patch storageclass gp2 -p '{"metadata":{"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'
kubectl apply -f - <<'EOF'
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gp3
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
provisioner: ebs.csi.aws.com
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
parameters:
  type: gp3
EOF
```

## Tear down

```bash
# Remove the release first so its load balancers and volumes are cleaned up.
helm uninstall hub -n kerberos-hub

terraform destroy
```

## Inputs

The defaults are tuned for a small test stack. See [variables.tf](variables.tf)
for the full list; the ones you are most likely to change:

| Variable | Default | Description |
| -------- | ------- | ----------- |
| `name` | `kerberos-hub` | Name prefix for every resource |
| `region` | `eu-west-1` | AWS region |
| `vpc_cidr` | `10.20.0.0/16` | VPC CIDR block |
| `single_nat_gateway` | `true` | One shared NAT gateway (cheaper, not highly available) |
| `kubernetes_version` | `1.31` | EKS control plane version |
| `cluster_endpoint_public_access_cidrs` | `["0.0.0.0/0"]` | Who may reach the Kubernetes API, **narrow this down** |
| `node_instance_types` | `["t3.large"]` | Worker node instance types |
| `node_desired_size` | `2` | Number of worker nodes |
| `docdb_instance_class` | `db.t3.medium` | DocumentDB instance class |
| `docdb_instance_count` | `1` | Number of DocumentDB instances |
| `docdb_username` | `kerberos` | Master username |
| `docdb_password` | generated | Master password, generated when unset |
| `docdb_tls` | `true` | Enforce TLS on the cluster |
| `docdb_allowed_cidrs` | `[]` | Extra CIDRs allowed on port 27017 |

## Outputs

| Output | Description |
| ------ | ----------- |
| `cluster_name`, `cluster_endpoint` | EKS cluster identity |
| `update_kubeconfig_command` | Ready to run `aws eks update-kubeconfig ...` |
| `vpc_id`, `private_subnet_ids` | Networking identifiers |
| `docdb_endpoint`, `docdb_reader_endpoint`, `docdb_port` | DocumentDB connection details |
| `docdb_username`, `docdb_password` | Master credentials (password is sensitive) |
| `mongodb_uri` | Connection string for `mongodb.uri` (sensitive) |
| `hub_values_snippet` | Ready to paste helm values including the TLS block (sensitive) |

## Related

- [`../amazon-documentdb`](../amazon-documentdb/README.md) — using DocumentDB as the Kerberos Hub metadata store
- [`../../overlays/documentdb`](../../overlays/documentdb) — Kustomize overlay that deploys Kerberos Hub against DocumentDB
- [`../../README.k8s-managed.md`](../../README.k8s-managed.md) — installing on managed Kubernetes