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+---
+title: "Migration from CHT 3.x to CHT 4.x in Kubernetes"
+linkTitle: "K8s Data Migration to 4.x"
+weight: 1
+description: >
+  Guide to migrate existing data from CHT 3.x to CHT 4.x in Kubernetes environments
+relatedContent: >
+---
+
+The hosting architecture differs entirely between CHT-Core 3.x and CHT-Core 4.x. When both versions are running in Kubernetes, migrating data requires specific steps using the [couchdb-migration](https://github.com/medic/couchdb-migration) tool. This tool interfaces with CouchDB to update shard maps and database metadata.
+
+{{% alert title="Note" %}}
+If after upgrading you get an error, `Cannot convert undefined or null to object` - please see [issue #8040](https://github.com/medic/cht-core/issues/8040) for a work around. This only affects CHT 4.0.0, 4.0.1, 4.1.0 and 4.1.1. It was fixed in CHT 4.2.0.
+{{% /alert %}}
+
+## Migration Steps
+
+1. Initial Setup
+```shell
+# Set your namespace
+NAMESPACE=<your-namespace>
+```
+
+2. Access the Source CouchDB (3.x)
+```shell
+# List all pods to find medic-os pod
+kubectl get pods -n $NAMESPACE
+
+# Access the medic-os pod
+kubectl exec -it -n $NAMESPACE <medic-os-pod-name> -- bash
+```
+
+3. Set Up Migration Tool Inside 3.x Pod
+
+Once inside the pod, install required dependencies:
+```shell
+# Add node apt repository and update apt
+curl -fsSL https://deb.nodesource.com/setup_16.x | bash -
+apt update
+
+# Ensure nodejs, npm and git are installed
+apt install -y nodejs npm git
+
+#  clone repository
+git clone https://github.com/medic/couchdb-migration.git
+cd couchdb-migration
+npm ci --omit=dev
+
+# Create a global symlink to enable running commands directly
+# Note: This may require sudo if npm's global directories aren't writable
+npm link
+```
+
+4. Run Pre-Migration Commands on 3.x
+
+While still `exec`ed in the `medic-os` container,  get credentials from 1Password and set them inside the pod:
+```shell
+export ADMIN_USER=<admin_username_from_1password>
+export ADMIN_PASSWORD=<admin_password_from_1password>
+
+# Set COUCH_URL
+export COUCH_URL="http://${ADMIN_USER}:${ADMIN_PASSWORD}@localhost:5984"
+
+# Verify connection
+curl -s $COUCH_URL/_up
+```
+
+Pre-index views to minimize downtime:
+```shell
+pre-index-views <desired CHT version>
+```
+
+{{% alert title="Note" %}} 
+If pre-indexing is omitted, 4.x API will fail to respond to requests until all views are indexed. For large databases, this could take many hours or days.
+{{% /alert %}}
+
+Save CouchDB configuration:
+```shell
+get-env
+```
+
+Save the output containing:
+- CouchDB secret (used for encrypting passwords and session tokens)
+- CouchDB server UUID (used for replication checkpointing)
+- CouchDB admin credentials
+
+You can now exit the medic-os container by running `exit`.
+
+5. Clone the 3.x Data Volume
+
+First, identify the volume ID from your 3.x data:
+```shell
+# Get the PVC name
+kubectl get pvc -n $NAMESPACE
+
+# Get the volume ID from the PVC
+VOLUME_ID=$(kubectl get pvc <your-3x-pvc-name> -n $NAMESPACE -o jsonpath='{.spec.volumeName}')
+EBS_VOLUME_ID=$(kubectl get pv $VOLUME_ID -o jsonpath='{.spec.awsElasticBlockStore.volumeID}' | cut -d'/' -f4)
+
+echo "Your 3.x EBS Volume ID is: $EBS_VOLUME_ID"
+
+# Create a snapshot of the 3.x volume
+SNAPSHOT_ID=$(aws ec2 create-snapshot \
+    --region eu-west-2 \
+    --volume-id $EBS_VOLUME_ID \
+    --description "CHT 3.x to 4.x migration snapshot" \
+    --query 'SnapshotId' \
+    --output text)
+
+echo "Created snapshot: $SNAPSHOT_ID"
+
+# Wait for the snapshot to complete
+aws ec2 wait snapshot-completed --snapshot-ids $SNAPSHOT_ID
+
+# Set cluster-specific variables
+# For development:
+AVAILABILITY_ZONE="eu-west-2b"
+CLUSTER_NAME="dev-cht-eks"
+
+# For production, comment out above and uncomment below:
+# AVAILABILITY_ZONE="eu-west-2a"
+# CLUSTER_NAME="prod-cht-eks"
+
+# Create a new volume from the snapshot
+NEW_VOLUME_ID=$(aws ec2 create-volume \
+    --region eu-west-2 \
+    --availability-zone $AVAILABILITY_ZONE \
+    --snapshot-id $SNAPSHOT_ID \
+    --volume-type gp2 \
+    --query 'VolumeId' \
+    --output text)
+
+echo "Created new volume: $NEW_VOLUME_ID"
+
+# Tag the new volume for Kubernetes use
+aws ec2 create-tags \
+    --resources $NEW_VOLUME_ID \
+    --tags Key=kubernetes.io/cluster/$CLUSTER_NAME,Value=owned Key=KubernetesCluster,Value=$CLUSTER_NAME
+
+# Verify your tags took effect
+aws ec2 describe-volumes --region eu-west-2 --volume-id $NEW_VOLUME_ID | jq '.Volumes[0].Tags'
+```
+
+6. Deploy CHT 4.x with Existing Data
+
+Create a `values.yaml` file using the volume ID from the previous step:
+
+For single node deployment:
+
+```yaml
+project_name: <your-namespace-defined-in-NAMESPACE>
+namespace: <your-namespace-defined-in-NAMESPACE>
+chtversion: 4.10.0  # Can be 4.10.0 or latest version
+
+upstream_servers:
+  docker_registry: "public.ecr.aws/medic"
+  builds_url: "https://staging.dev.medicmobile.org/_couch/builds_4"
+
+couchdb:
+  password: <from_get-env_command>  # Avoid using non-url-safe characters
+  secret: <from_get-env_command>
+  user: <admin_user>
+  uuid: <from_get-env_command>
+  clusteredCouch_enabled: false
+  couchdb_node_storage_size: 100Mi
+
+toleration:  # For production, change key to "prod-couchdb-only"
+  key: "dev-couchdb-only"
+  operator: "Equal"
+  value: "true"
+  effect: "NoSchedule"
+
+ingress:
+  annotations:  # For production, update groupname to "prod-cht-alb" and Environment to "prod"
+    groupname: "dev-cht-alb"
+    tags: "Environment=dev,Team=QA"
+    certificate: "arn:aws:iam::<account-id>:server-certificate/2024-wildcard-dev-medicmobile-org-chain"
+  host: <your-url>  # eg. yyyy.app.medicmobile.org
+  hosted_zone_id: <your-hosted-zone-id>
+  # For production, use the production load balancer address
+  load_balancer: "dualstack.k8s-devchtalb-3eb0781cbb-694321496.eu-west-2.elb.amazonaws.com"
+
+environment: "remote"
+cluster_type: "eks"
+cert_source: "eks-medic"
+
+couchdb_data:
+  preExistingDataAvailable: "true"
+  dataPathOnDiskForCouchDB: "storage/medic-core/couchdb/data"  # Use subPath from 3.x instance
+  partition: "0"
+
+ebs:
+  preExistingEBSVolumeID-1: <NEW_VOLUME_ID-from-previous-step>  # Volume containing 3.x data
+  preExistingEBSVolumeSize: "100Gi"
+
+```
+
+For a clustered deployment.
+
+```yaml
+project_name: <your-namespace-defined-in-NAMESPACE>
+namespace: <your-namespace-defined-in-NAMESPACE>
+chtversion: 4.10.0  # Can be 4.10.0 or latest version
+
+upstream_servers:
+  docker_registry: "public.ecr.aws/medic"
+  builds_url: "https://staging.dev.medicmobile.org/_couch/builds_4"
+upgrade_service:
+  tag: 0.32
+
+couchdb:
+  password: <from_get-env_command>  # Avoid using non-url-safe characters
+  secret: <from_get-env_command>
+  user: <admin_user>
+  uuid: <from_get-env_command>
+  clusteredCouch_enabled: true  # Set to true if you want clustered CouchDB in 4.x
+  couchdb_node_storage_size: 100Mi #Set equal to the migrated disk
+
+clusteredCouch:  # Only relevant if clusteredCouch_enabled is true
+  noOfCouchDBNodes: 3
+
+toleration:  # For production, change key to "prod-couchdb-only"
+  key: "dev-couchdb-only"
+  operator: "Equal"
+  value: "true"
+  effect: "NoSchedule"
+
+ingress:
+  annotations:  # For production, update groupname to "prod-cht-alb" and Environment to "prod"
+    groupname: "dev-cht-alb"
+    tags: "Environment=dev,Team=QA"
+    certificate: "arn:aws:iam::<account-id>:server-certificate/2024-wildcard-dev-medicmobile-org-chain"
+  host: <your-url>  # eg. yyyy.app.medicmobile.org
+  hosted_zone_id: <your-hosted-zone-id>
+  # For production, use the production load balancer address
+  load_balancer: "dualstack.k8s-devchtalb-3eb0781cbb-694321496.eu-west-2.elb.amazonaws.com"
+
+environment: "remote"
+cluster_type: "eks"
+cert_source: "eks-medic"
+
+# Only need to specify nodes if deploying on k3s and want to use specific nodes for CouchDB pods
+#nodes:
+#  node-1: <worker-node-1-name>  # Only for k3s deployments
+#  node-2: <worker-node-2-name>  # Only for k3s deployments
+#  node-3: <worker-node-3-name>  # Only for k3s deployments
+
+couchdb_data:
+  preExistingDataAvailable: "true"
+  dataPathOnDiskForCouchDB: "storage/medic-core/couchdb/data"  # Use subPath from 3.x instance
+  partition: "0"
+
+ebs:
+  preExistingEBSVolumeID-1: <NEW_VOLUME_ID-from-previous-step>  # Volume containing 3.x data
+  preExistingEBSVolumeID-2: ""  # Leave empty for secondary nodes
+  preExistingEBSVolumeID-3: ""  # Leave empty for tertiary nodes
+  preExistingEBSVolumeSize: "100Gi" #Set equal to the migrated disk
+```
+
+Deploy using cht-deploy script from cht-core repository:
+```shell
+cd cht-core/scripts/deploy
+./cht-deploy -f PATH_TO/values.yaml
+```
+
+7. Verify Deployment and Run Migration Commands
+
+First verify CouchDB is running properly:
+```shell
+# Check pod status
+kubectl get pods -n $NAMESPACE
+
+# For single node check CouchDB is up
+kubectl exec -it -n $NAMESPACE $(kubectl get pod -n $NAMESPACE -l cht.service=couchdb -o name) -- \
+  curl -s http://localhost:5984/_up
+
+# For clustered setup (check all nodes)
+kubectl exec -it -n $NAMESPACE $(kubectl get pod -n $NAMESPACE -l cht.service=couchdb-1 -o name) -- \
+  curl -s http://localhost:5984/_up
+```
+
+Access the new CouchDB pod based on your deployment type.
+
+For single node:
+```shell
+kubectl exec -it -n $NAMESPACE $(kubectl get pod -n $NAMESPACE -l cht.service=couchdb -o name) -- bash
+```
+
+For clustered setup (always use couchdb-1):
+```shell
+kubectl exec -it -n $NAMESPACE $(kubectl get pod -n $NAMESPACE -l cht.service=couchdb-1 -o name) -- bash
+```
+
+Once inside the pod, set up the migration tool again:
+```shell
+curl -fsSL https://deb.nodesource.com/setup_16.x | bash -
+apt install -y nodejs npm git
+git clone https://github.com/medic/couchdb-migration.git
+cd couchdb-migration
+npm ci --omit=dev
+
+# Create a global symlink to enable running commands directly
+# Note: This may require sudo if npm's global directories aren't writable
+npm link
+
+# Set up CouchDB connection
+export ADMIN_USER=<admin_username_from_1password>
+export ADMIN_PASSWORD=<admin_password_from_1password>
+export COUCH_URL="http://${ADMIN_USER}:${ADMIN_PASSWORD}@localhost:5984"
+
+# Verify CouchDB is up and responding
+check-couchdb-up
+```
+
+For single node deployment:
+```shell
+move-node
+verify
+```
+
+For clustered deployment:
+```shell
+# Generate distribution matrix
+shard_matrix=$(generate-shard-distribution-matrix)
+
+# Get movement instructions
+shard-move-instructions $shard_matrix
+
+{{% alert title="Note" %}}
+For clustered setups, shards must be moved both in software (using the migration commands) and physically (the actual data must be moved between EBS volumes). Follow the instructions from shard-move-instructions carefully.
+{{% /alert %}}
+
+# After moving shards according to instructions
+move-shards $shard_matrix
+
+# Remove old node from cluster
+remove-node couchdb@127.0.0.1
+
+# Verify the migration
+verify
+```