add doc for migration with data move

docs/multi-instance.md

@@ -8,13 +8,89 @@ See [554#issuecomment-496804929](https://github.com/elastic/ansible-elasticsearc
 
 If you have single-instances hosts and want to upgrade from previous versions of the role:
 
+### Procedure with data move
+
+This procedure will allow you to move your data to the new standard paths (see [#581](https://github.com/elastic/ansible-elasticsearch/issues/581)):
+
+1. Stop Elasticsearch before the migration
+
+2. Migrate your data to the new standard paths:
+```
+# mv /etc/elasticsearch/${ES_INSTANCE_NAME}/* /etc/elasticsearch/ && rm -fr /etc/elasticsearch/${ES_INSTANCE_NAME}/
+mv: overwrite '/etc/elasticsearch/elasticsearch.keystore'? y
+# mv /var/lib/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/* /var/lib/elasticsearch/ && rm -fr /var/lib/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+# ls /var/lib/elasticsearch/
+nodes
+# mv /var/log/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/* /var/log/elasticsearch/ && rm -fr /var/log/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+# rm -fr /var/run/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+```
+
+3. Update playbook (remove `es_conf_dir`, `es_data_dirs`, `es_log_dir`, `es_pid_dir` and `es_instance_name` variables)
+
+4. Update ansible-role to new version ([7.1.1](https://github.com/elastic/ansible-elasticsearch/releases/tag/7.1.1) at the time of writing) and deploy ansible-role
+
+5. After ansible-role new deployment, you can do some cleanup of old Init file and Default file:
+
+Example:
+```
+$ systemctl stop elasticsearch
+$ mv /etc/elasticsearch/${ES_INSTANCE_NAME}/* /etc/elasticsearch/ && rm -fr /etc/elasticsearch/${ES_INSTANCE_NAME}/
+mv: overwrite '/etc/elasticsearch/elasticsearch.keystore'? y
+$ mv /var/lib/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/* /var/lib/elasticsearch/ && rm -fr /var/lib/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+$ ls /var/lib/elasticsearch/
+nodes
+$ mv /var/log/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/* /var/log/elasticsearch/ && rm -fr /var/log/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+$ rm -fr /var/run/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}/
+$ ansible-galaxy install --force elastic.elasticsearch,7.1.1
+- changing role elastic.elasticsearch from 6.6.0 to 7.1.1
+- downloading role 'elasticsearch', owned by elastic
+- downloading role from https://github.com/elastic/ansible-elasticsearch/archive/7.1.1.tar.gz
+- extracting elastic.elasticsearch to /home/jmlrt/.ansible/roles/elastic.elasticsearch
+- elastic.elasticsearch (7.1.1) was installed successfully
+$ ansible-playbook playbook.yml
+
+...
+
+TASK [elastic.elasticsearch : Create Directories]
+ok: [localhost] => (item=/var/run/elasticsearch)
+ok: [localhost] => (item=/var/log/elasticsearch)
+changed: [localhost] => (item=/etc/elasticsearch)
+ok: [localhost] => (item=/var/lib/elasticsearch)
+
+TASK [elastic.elasticsearch : Copy Configuration File]
+changed: [localhost]
+
+TASK [elastic.elasticsearch : Copy Default File]
+changed: [localhost]
+
+TASK [elastic.elasticsearch : Copy jvm.options File]
+changed: [localhost]
+
+...
+
+RUNNING HANDLER [elastic.elasticsearch : restart elasticsearch]
+changed: [localhost]
+
+...
+
+PLAY RECAP
+localhost                  : ok=26   changed=6    unreachable=0    failed=0    skipped=116  rescued=0    ignored=0
+$ find /etc -name '${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}*'
+/etc/default/node1_elasticsearch
+/etc/systemd/system/multi-user.target.wants/node1_elasticsearch.service
+```
+
+### Procedure without data move
+
+This procedure will allow you to keep your data to the old paths:
+
 1. Override these variables to match previous values:
 ```yaml
-es_conf_dir: /etc/elasticsearch/{{ es_instance_name }}
+es_conf_dir: /etc/elasticsearch/${ES_INSTANCE_NAME}
 es_data_dirs:
-  - /var/lib/elasticsearch/{{ inventory_hostname }}-{{ es_instance_name }}
-es_log_dir: /var/log/elasticsearch/{{ inventory_hostname }}-{{ es_instance_name }}
-es_pid_dir: /var/run/elasticsearch/{{ inventory_hostname }}-{{ es_instance_name }}
+  - /var/lib/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}
+es_log_dir: /var/log/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}
+es_pid_dir: /var/run/elasticsearch/${INVENTORY_HOSTNAME}-${ES_INSTANCE_NAME}
 ```
 
 2. Deploy ansible-role. **Even if these variables are overrided, Elasticsearch config file and default option file will change, which imply an Elasticsearch restart.**