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Highly Available Cluster Setup

You can run three Dgraph Alpha servers and three Dgraph Zero servers in a highly available cluster setup. For a highly available setup, start the Dgraph Zero server with --replicas 3 flag, so that all data is replicated on three Alpha servers and forms one Alpha group. You can install a highly available cluster using:

dgraph-ha.yaml file
Helm charts.

Install a highly avaiable Dgraph cluster using YAML or Helm

Before you begin:

Install kubectl.
Ensure that you have a production-ready Kubernetes cluster with atleast three worker nodes running in a cloud provider of your choice.
(Optional) To run Dgraph Alpha with TLS, see TLS Configuration.

Installing a highly available Dgraph cluster

Verify that you are able to access the nodes in the Kubernetes cluster:

kubectl get nodes

An output similar to this appears:

  NAME                                          STATUS   ROLES    AGE   VERSION
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf

After your Kubernetes cluster is up, you can use dgraph-ha.yaml to start the cluster.

Start a StatefulSet that creates Pods with Zero, Alpha, and Ratel UI:

kubectl create --filename https://raw.githubusercontent.com/dgraph-io/dgraph/main/contrib/config/kubernetes/dgraph-ha/dgraph-ha.yaml

An output similar to this appears:

service/dgraph-zero-public created
service/dgraph-alpha-public created
service/dgraph-ratel-public created
service/dgraph-zero created
service/dgraph-alpha created
statefulset.apps/dgraph-zero created
statefulset.apps/dgraph-alpha created
deployment.apps/dgraph-ratel created

Confirm that the Pods were created successfully.

kubectl get pods

An output similar to this appears:

 NAME                  READY   STATUS    RESTARTS   AGE
dgraph-alpha-0        1/1     Running   0          6m24s
dgraph-alpha-1        1/1     Running   0          5m42s
dgraph-alpha-2        1/1     Running   0          5m2s
dgraph-ratel-<pod-id> 1/1     Running   0          6m23s
dgraph-zero-0         1/1     Running   0          6m24s
dgraph-zero-1         1/1     Running   0          5m41s
dgraph-zero-2         1/1     Running   0          5m6s

You can check the logs for the Pod using kubectl logs --follow <POD_NAME>..

Port forward from your local machine to the Pod:

   kubectl port-forward service/dgraph-alpha-public 8080:8080
   kubectl port-forward service/dgraph-ratel-public 8000:8000

Go to http://localhost:8000 to access Dgraph using the Ratel UI.

Note You can also access the service on its External IP address.

Deleting highly available Dgraph resources

Delete all the resources using:

kubectl delete --filename https://raw.githubusercontent.com/dgraph-io/dgraph/main/contrib/config/kubernetes/dgraph-ha/dgraph-ha.yaml
kubectl delete persistentvolumeclaims --selector app=dgraph-zero
kubectl delete persistentvolumeclaims --selector app=dgraph-alpha

Before you begin

Install kubectl.
Ensure that you have a production-ready Kubernetes cluster with atleast three worker nodes running in a cloud provider of your choice.
Install Helm.
(Optional) To run Dgraph Alpha with TLS, see TLS Configuration.

Installing a highly available Dgraph cluster using Helm

Verify that you are able to access the nodes in the Kubernetes cluster:

kubectl get nodes

An output similar to this appears:

  NAME                                          STATUS   ROLES    AGE   VERSION
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf
 <aws-ip-hostname>.<region>.compute.internal   Ready    <none>   1m   v1.15.11-eks-af3caf

After your Kubernetes cluster is up and running, you can use of the Dgraph Helm chart to install a highly avaiable Dgraph cluster

Add the Dgraph helm repository::

helm repo add dgraph https://charts.dgraph.io

Install the chart with <RELEASE-NAME>:

helm install <RELEASE-NAME> dgraph/dgraph

You can also specify the version using:

   helm install <RELEASE-NAME> dgraph/dgraph --set image.tag="main"

When configuring the Dgraph image tag, be careful not to use latest or main in a production environment. These tags may have the Dgraph version change, causing a mixed-version Dgraph cluster that can lead to an outage and potential data loss.

An output similar to this appears:

 ```bash
 NAME: <RELEASE-NAME>
 LAST DEPLOYED: Wed Feb  1 21:26:32 2023
 NAMESPACE: default
 STATUS: deployed
 REVISION: 1
 TEST SUITE: None
 NOTES:
 1. You have just deployed Dgraph, version 'v21.12.0'.

    For further information:
     * Documentation: https://dgraph.io/docs/
     * Community and Issues: https://discuss.dgraph.io/   
 2. Get the Dgraph Alpha HTTP/S endpoint by running these commands.
    export ALPHA_POD_NAME=$(kubectl get pods --namespace default --selector "statefulset.kubernetes.io/pod-name=<RELEASE-NAME>-dgraph-alpha-0,release=<RELEASE-NAME>-dgraph" --output jsonpath="{.items[0].metadata.name}")
    echo "Access Alpha HTTP/S using http://localhost:8080"
    kubectl --namespace default port-forward $ALPHA_POD_NAME 8080:8080

   NOTE: Change "http://" to "https://" if TLS was added to the Ingress, Load Balancer, or Dgraph Alpha service.
 ```

Get the name of the Pods in the cluster using kubectl get pods:

   NAME                          READY   STATUS    RESTARTS   AGE
  <RELEASE-NAME>-dgraph-alpha-0   1/1     Running   0          4m48s
  <RELEASE-NAME>-dgraph-alpha-1   1/1     Running   0          4m2s
  <RELEASE-NAME>-dgraph-alpha-2   1/1     Running   0          3m31s
  <RELEASE-NAME>-dgraph-zero-0    1/1     Running   0          4m48s
  <RELEASE-NAME>-dgraph-zero-1    1/1     Running   0          4m10s
  <RELEASE-NAME>-dgraph-zero-2    1/1     Running   0          3m50s

Get the Dgraph Alpha HTTP/S endpoint by running these commands:

    export ALPHA_POD_NAME=$(kubectl get pods --namespace default --selector "statefulset.kubernetes.io/pod-name=<RELEASE-NAME>-dgraph-alpha-0,release=<RELEASE-NAME>-dgraph" --output jsonpath="{.items[0].metadata.name}")
    echo "Access Alpha HTTP/S using http://localhost:8080"
    kubectl --namespace default port-forward $ALPHA_POD_NAME 8080:8080

Deleting the resources from the cluster

Delete the Helm deployment using:
```
  helm delete my-release
```

Delete associated Persistent Volume Claimss:

kubectl delete pvc --selector release=my-release

Dgraph configuration files

You can create a Dgraph Config files for Alpha server and Zero server with Helm chart configuration values, <MY-CONFIG-VALUES>. For more information about the values, see the latest configuration settings.

Open an editor of your choice and create a config file named <MY-CONFIG-VALUES>.yaml:

# <MY-CONFIG-VALUES>.yaml
alpha:
  configFile:
    config.yaml: |
      alsologtostderr: true
      badger:
        compression_level: 3
        tables: mmap
        vlog: mmap
      postings: /dgraph/data/p
      wal: /dgraph/data/w      
zero:
  configFile:
    config.yaml: |
      alsologtostderr: true
      wal: /dgraph/data/zw

Change to the director in which you created <MY-CONFIG-VALUES>.yaml and then install with Alpha and Zero configuration using:

helm install <RELEASE-NAME> dgraph/dgraph --values <MY-CONFIG-VALUES>.yaml

Exposing Alpha and Ratel Services

By default Zero and Alpha services are exposed only within the Kubernetes cluster as Kubernetes service type ClusterIP.

In order to expose the Alpha service and Ratel service publicly you can use Kubernetes service type LoadBalancer or an Ingress resource.

Public Internet

To use an external load balancer, set the service type to LoadBalancer.

Note For security purposes we recommend limiting access to any public endpoints, such as using a white list.

To expose Alpha service to the Internet use:

helm install <RELEASE-NAME> dgraph/dgraph --set alpha.service.type="LoadBalancer"

To expose Alpha and Ratel services to the Internet use:

helm install <RELEASE-NAME> dgraph/dgraph --set alpha.service.type="LoadBalancer" --set ratel.service.type="LoadBalancer"

Private Internal Network

An external load balancer can be configured to face internally to a private subnet rather the public Internet. This way it can be accessed securely by clients on the same network, through a VPN, or from a jump server. In Kubernetes, this is often configured through service annotations by the provider. Here’s a small list of annotations from cloud providers:

Provider	Documentation Reference	Annotation
AWS	Amazon EKS: Load Balancing	`service.beta.kubernetes.io/aws-load-balancer-internal: "true"`
Azure	AKS: Internal Load Balancer	`service.beta.kubernetes.io/azure-load-balancer-internal: "true"`
Google Cloud	GKE: Internal Load Balancing	`cloud.google.com/load-balancer-type: "Internal"`

As an example, using Amazon EKS as the provider.

Create a Helm chart configuration values file <MY-CONFIG-VALUES>.yaml file:

# <MY-CONFIG-VALUES>.yaml
alpha:
  service:
    type: LoadBalancer
    annotations:
      service.beta.kubernetes.io/aws-load-balancer-internal: "true"
ratel:
  service:
    type: LoadBalancer
    annotations:
      service.beta.kubernetes.io/aws-load-balancer-internal: "true"

To expose Alpha and Ratel services privately, use:

helm install <RELEASE-NAME> dgraph/dgraph --values <MY-CONFIG-VALUES>.yaml

You can expose Alpha and Ratel using an ingress resource that can route traffic to service resources. Before using this option you may need to install an ingress controller first, as is the case with AKS and EKS, while in the case of GKE, this comes bundled with a default ingress controller. When routing traffic based on the hostname, you may want to integrate an addon like ExternalDNS so that DNS records can be registered automatically when deploying Dgraph.

As an example, you can configure a single ingress resource that uses ingress-nginx for Alpha and Ratel services.

Create a Helm chart configuration values file, <MY-CONFIG-VALUES>.yaml file:

# <MY-CONFIG-VALUES>.yaml
global:
  ingress:
    enabled: false
    annotations:
      kubernetes.io/ingress.class: nginx
    ratel_hostname: "ratel.<my-domain-name>"
    alpha_hostname: "alpha.<my-domain-name>"

To expose Alpha and Ratel services through an ingress:

helm install <RELEASE-NAME> dgraph/dgraph --values <MY-CONFIG-VALUES>.yaml

You can run kubectl get ingress to see the status and access these through their hostname, such as http://alpha.<my-domain-name> and http://ratel.<my-domain-name>

Tip Ingress controllers will likely have an option to configure access for private internal networks. Consult documentation from the ingress controller provider for further information.

Upgrading the Helm chart

You can update your cluster configuration by updating the configuration of the Helm chart. Dgraph is a stateful database that requires some attention on upgrading the configuration carefully in order to update your cluster to your desired configuration.

In general, you can use helm upgrade to update the configuration values of the cluster. Depending on your change, you may need to upgrade the configuration in multiple steps.

To upgrade to an HA cluster setup:

Ensure that the shard replication setting is more than one and zero.shardReplicaCount. For example, set the shard replica flag on the Zero node group to 3,zero.shardReplicaCount=3.
Run the Helm upgrade command to restart the Zero node group:
```
helm upgrade <RELEASE-NAME> dgraph/dgraph [options]
```
Set the Alpha replica count flag. For example: alpha.replicaCount=3.

Run the Helm upgrade command again:

helm upgrade <RELEASE-NAME> dgraph/dgraph [options]