added: jenkins migration

Author: imShakil

projects/jenkins/migration/migration.md

@@ -0,0 +1,86 @@
+# Migrating Jenkins Container from One Host To Another
+
+## Caution
+
+- Identify the Jenkins version you are using, it should be the same image on the new host
+- Both server should be able to communicate with each other usin SSH
+
+## Identity Jenkins Home Directory
+
+On your current server, find the volume used to persist jenkins data. If you are using bind mounts volume try to find the location using following command:
+
+```shell
+docker inspect jenkins-container-name | grep volume
+```
+
+of if using docker named volume:
+
+```shell
+docker volume ls
+```
+
+## Backup Jenkins Data
+
+Before creating a backup, make sure jenkins server stopped:
+
+```shell
+docker stop jenkins-container-name
+```
+
+Archive the jenkins home data:
+
+```shell
+tar -czvf jenkins_backup.tar.gz /path/of/bind/mount
+```
+
+If it's a named volume:
+
+```shell
+docker run --rm -v jenkins_home:/data -v $(pwd):/backup alpine \
+tar czvf /backup/jenkins_backup.tar.gz -C /data .
+```
+
+> Here, we have used a new container using `alpine` image to create a backup of `jenkins` docker volume. it will create a `jenkins_backup.tar.gz` file in your current directory.
+
+## Transfer to New Server
+
+Copy the backup file to new server:
+
+```shell
+scp jenkins_backup.tar.gz user@new_host:/path/to/new_host
+```
+
+## Restore Data
+
+You can extract data into a directory to use as bind mount or a docker volume. 
+
+To extract into a directory:
+
+```shell
+mkdir -p /var/jenkins_home
+tar -xzvf jenkins_backup.tar.gz -C /var/jenkins_home
+chown -R 1000:1000 /var/jenkins_home
+```
+
+To extract into a docker volume:
+
+```shell
+# create docker volume
+docker volume create jenkins_home
+
+# extract data into this volume and fix file permissions
+docker run --rm -v jenkins_home:/data -v /directory_path/of/backup_file/:/backup alpine \
+sh -c "cd /data && tar xzvf /backup/jenkins_backup.tar.gz && chown -R 1000:1000 /data"
+```
+
+> What's happening here?: docker creating a new alpine container using jenkins_home volume, and extracted backup data into that directory and modified the files permission.
+
+## Run Jenkins on the New Host
+
+Let's run the jenkins container on the new host with resorted data volume.
+
+```shell
+docker run -d --name jenkins -p 8080:8080 -p 50000:50000 -v jenkins_home:/var/jenkins_home jenkins/jenkins:lts
+```
+
+We are done.