Use PD Recover to Recover the PD Cluster

PD Recover is a disaster recovery tool of PD, used to recover the PD cluster which cannot start or provide services normally.

Download PD Recover

Download the official TiDB package:
```
wget https://download.pingcap.org/tidb-${version}-linux-amd64.tar.gz
```
In the command above, ${version} is the version of the TiDB cluster, such as v4.0.0-rc.
Unpack the TiDB package for installation:
```
tar -xzf tidb-${version}-linux-amd64.tar.gz
```
pd-recover is in the tidb-${version}-linux-amd64/bin directory.

Recover the PD cluster

This section introduces how to recover the PD cluster using PD Recover.

Get Cluster ID

kubectl get tc ${cluster_name} -n ${namespace} -o='go-template={{.status.clusterID}}{{"\n"}}'

Example:

kubectl get tc test -n test -o='go-template={{.status.clusterID}}{{"\n"}}'
6821434242797747735

Get Alloc ID

When you use pd-recover to recover the PD cluster, you need to specify alloc-id. The value of alloc-id must be larger than the largest allocated ID (Alloc ID) of the original cluster.

Access the Prometheus monitoring data of the TiDB cluster by taking steps in Access the monitoring data.
Enter pd_cluster_id in the input box and click the Execute button to make a query. Get the largest value in the query result.
Multiply the largest value in the query result by 100. Use the multiplied value as the alloc-id value specified when using pd-recover.

Recover the PD Pod

Delete the Pod of the PD cluster.
Execute the following command to set the value of spec.pd.replicas to 0:
```
kubectl edit tc ${cluster_name} -n ${namespace}
```
Because the PD cluster is in an abnormal state, TiDB Operator cannot synchronize the change above to the PD StatefulSet. You need to execute the following command to set the spec.replicas of the PD StatefulSet to 0.
```
kubectl edit sts ${cluster_name}-pd -n ${namespace}
```
Execute the following command to confirm that the PD Pod is deleted:
```
kubectl get pod -n ${namespace}
```
After confirming that all PD Pods are deleted, execute the following command to delete the PVCs bound to the PD Pods:
```
kubectl delete pvc -l app.kubernetes.io/component=pd,app.kubernetes.io/instance=${cluster_name} -n ${namespace}
```
After the PVCs are deleted, scale out the PD cluster to one Pod:
Execute the following command to set the value of spec.pd.replicas to 1:
```
kubectl edit tc ${cluster_name} -n ${namespace}
```
Because the PD cluster is in an abnormal state, TiDB Operator cannot synchronize the change above to the PD StatefulSet. You need to execute the following command to set the spec.replicas of the PD StatefulSet to 1.
```
kubectl edit sts ${cluster_name}-pd -n ${namespace}
```
Execute the following command to confirm that the PD Pod is started:
```
kubectl get pod -n ${namespace}
```

Recover the cluster

Execute the port-forward command to expose the PD service:

kubectl port-forward -n ${namespace} svc/${cluster_name}-pd 2379:2379

Open a new terminal tab or window, enter the directory where pd-recover is located, and execute the pd-recover command to recover the PD cluster:
```
./pd-recover -endpoints http://127.0.0.1:2379 -cluster-id ${cluster_id} -alloc-id ${alloc_id}
```
In the command above, ${cluster_id} is the cluster ID got in Get Cluster ID. ${alloc_id} is the largest value of pd_cluster_id (got in Get Alloc ID) multiplied by 100.
After the pd-recover command is successfully executed, the following result is printed:
```
recover success! please restart the PD cluster
```
Go back to the window where the port-forward command is executed, press Ctrl+C to stop and exit.

Restart the PD Pod

Delete the PD Pod:

kubectl delete pod ${cluster_name}-pd-0 -n ${namespace}

After the Pod is started successfully, execute the port-forward command to expose the PD service:
```
kubectl port-forward -n ${namespace} svc/${cluster_name}-pd 2379:2379
```
Open a new terminal tab or window, execute the following command to confirm the Cluster ID is the one got in Get Cluster ID.
```
curl 127.0.0.1:2379/pd/api/v1/cluster
```
Go back to the window where the port-forward command is executed, press Ctrl+C to stop and exit.

Increase the capacity of the PD cluster

Execute the following command to set the value of spec.pd.replicas to the desired number of Pods:

kubectl edit tc ${cluster_name} -n ${namespace}

Restart TiDB and TiKV

kubectl delete pod -l app.kubernetes.io/component=tidb,app.kubernetes.io/instance=${cluster_name} -n ${namespace} &&
kubectl delete pod -l app.kubernetes.io/component=tikv,app.kubernetes.io/instance=${cluster_name} -n ${namespace}