chore(maindbv4): add a migration guide

docs/v2-2-0-migration-guide.md

@@ -0,0 +1,181 @@
+# MainDB v4 Migration Paths
+
+## Introduction
+
+The `v2.2.0` release introduces database and SQLite changes to improve performance and storage. This document outlines the possible
+migration paths.
+
+**Note:** The examples below assume you are operating a node on mainnet.
+
+## Table of Contents
+
+- [Blue / Green Deployment](#blue--green-deployment)
+- [Sync in Parallel](#sync-in-parallel)
+    - [1. Docker Migration](#1-docker-migration)
+    - [2. Manual Migration](#2-manual-migration)
+- [Install Latest Version](#install-latest-version)
+    - [Using Docker](#using-docker)
+    - [Install From Source](#install-from-source)
+
+## Blue / Green Deployment
+
+- For environments implementing a blue/green deployment strategy , starting a new node with the update image and allowing it to
+  sync before a switching traffic is a seamless approach. Once synced, traffic can be directed towards to the new node, and the
+  old node can be stopped.
+
+## Sync in Parallel
+
+- Syncing in parallel minimizes downtime but requires additional CPU, RAM and storage resources.
+
+### 1. Docker Migration
+
+For setups where Docker volumes are mapped to a location on the host machine.
+
+**Note**: The examples assume the default data directory within the container is used. If a custom directory is configured,
+adjustments to the examples are required.
+
+For an existing node with a host instance directory of `/path/to/thor`:
+
+```html
+docker run -d \
+   -v /path/to/thor:/home/thor/.org.vechain.thor 
+   -p 8669:8669 \
+   -p 11235:11235 \
+   --name <your-container-name> \
+   vechain/thor:v2.1.4 --network main <additional-flags>
+```
+
+Start a new container with `v2.2.0`, without exposing the ports:
+
+```html
+docker run -d \
+   -v /path/to/thor:/home/thor/.org.vechain.thor 
+   --name node-new \
+   vechain/thor:v2.2.0 --network main <additional-flags>
+```
+
+- The `v2.1.4` node will continue to operate and write data to the directory `/path/to/thor/instance-39627e6be7ec1b4a-v3`, while the
+  `v2.2.0` node will write the new databases to `/path/to/thor/instance-39627e6be7ec1b4a-v4`.
+- Allow some time for the new node to sync.
+- You can inspect the logs using `docker logs --tail 25 node-new`.
+- After the new node is fully synced, stop both nodes and restart the original container with the updated image.
+
+```html
+docker stop node-new
+docker rm node-new
+docker stop <container-name>
+docker rm <container-name>
+
+docker run -d \
+   -v /path/to/thor:/home/thor/.org.vechain.thor 
+   -p 8669:8669 \
+   -p 11235:11235 \
+   --name <your-container-name> \
+   vechain/thor:v2.2.0 --network main <additional-flags>
+```
+
+- Confirm that the node is functioning as expected, before cleaning up the old databases:
+
+```bash
+rm -rf /path/to/thor/instance-39627e6be7ec1b4a-v3
+```
+
+### 2. Manual Migration
+
+For nodes that installed from the source, follow the steps below:
+
+- Assuming the old nodes was started with:
+
+```html
+/previous/executable/thor --network main <additional-flags>
+```
+
+- Build the new `thor` binary as outlined in [Install From Source](#install-from-source)
+
+- Start the new node with different API, Metrics, Admin and P2P ports:
+
+```html
+./bin/thor --network main \
+    --api-addr localhost:8668 \
+    --metrics-addr localhost:2102 \
+    --admin-addr localhost:2103 \
+    --p2p-port 11222 \
+    <additional-flags>
+```
+
+- The `v2.1.4` node will continue to operate and write data to the data directory under `/data/dir/instance-39627e6be7ec1b4a-v3`, while
+  `v2.2.0` node writes to `/data/dir/instance-39627e6be7ec1b4a-v4`.
+- Allow the new node to sync before switching traffic.
+
+#### Stopping and Switching Nodes
+
+##### 1. Get the PID of the new node:
+
+```html
+lsof -n -i:8668
+```
+
+##### 2. Stop the new node:
+
+```html
+kill <pid>
+```
+
+##### 3. Get the PID of the old node:
+
+```html
+lsof -n -i:8669
+```
+
+##### 4. Stop the old node:
+
+```html
+kill <pid>
+```
+
+##### 5. Restart the original node command with the new binary:
+
+```html
+/new/executable/thor --network main <additional-flags>
+```
+
+##### 6. Remove the old databases:
+
+```bash
+rm -rf /data/dir/instance-39627e6be7ec1b4a-v3
+```
+
+## Install Latest Version
+
+### Using Docker
+
+```bash
+docker pull vechain/thor:v2.2.0
+```
+
+### Install From Source
+
+- Clone the repository and checkout the `v2.2.0` tag:
+
+```bash
+git clone https://github.com/vechain/thor.git --branch v2.2.0 --depth 1
+```
+
+- Build the `thor` binary:
+
+```bash
+cd thor
+make thor
+```
+
+- Verify the binary:
+
+```bash
+./bin/thor --version
+```
+
+- (Optional), Copy the binary to a location in your `$PATH`:
+
+```bash
+sudo cp ./bin/thor /usr/local/bin
+```