Fix RabbitMQ backup on RHEL/CentOS (#2923)

* Install python3 on all hosts (RHEL/CentOS)

* Add note about workaround

* Update changelog

Author: to-bar

CHANGELOG-1.0.md

@@ -2,6 +2,11 @@
 
 ## [1.0.2] 2021-xx-xx
 
+### NOTE ###
+
+Before running `epicli backup` for RHEL/CentOS based cluster with standalone (non-K8s) RabbitMQ component,
+read note in [this doc](docs/home/howto/BACKUP.md#1-how-to-perform-backup).
+
 ### Added
 
 - [#2124](https://github.com/epiphany-platform/epiphany/issues/2124) - Added Internet connection test to download-requirements.sh
@@ -14,6 +19,7 @@
 
 ### Fixed
 
+- [#2920](https://github.com/epiphany-platform/epiphany/issues/2920) - [RHEL/CentOS] RabbitMQ backup fails: /usr/bin/env: python3: No such file or directory
 - [#2425](https://github.com/epiphany-platform/epiphany/issues/2425) - Feature-mapping - 'enabled: no' do nothing
 - [#1294](https://github.com/epiphany-platform/epiphany/issues/1294) - Implement proper merging of lists of dictionaries for epicli yaml docs
 - [#1370](https://github.com/epiphany-platform/epiphany/issues/1370) - Epicli does not correctly generate vars for Postgres

core/src/epicli/data/common/ansible/playbooks/roles/common/tasks/RedHat.yml

@@ -33,6 +33,7 @@
       - net-tools
       - openssl
       - python-setuptools
+      - python3
       - rsync
       - sysstat
       - tar

core/src/epicli/data/common/ansible/playbooks/roles/repository/files/download-requirements/centos-7/requirements.txt

@@ -93,6 +93,7 @@ python-slip-dbus # for firewalld
 python-ipaddress
 python-backports
 python2-cryptography # for Ansible (certificate modules)
+python3-3.6.*
 quota # for nfs-utils
 rabbitmq-server-3.8.9
 rh-haproxy18

core/src/epicli/data/common/ansible/playbooks/roles/repository/files/download-requirements/redhat-7/requirements.txt

@@ -89,6 +89,7 @@ python-pycparser # for python2-cryptography
 python-setuptools
 python-slip-dbus # for firewalld
 python2-cryptography # for Ansible (certificate modules)
+python3-3.6.*
 quota # for nfs-utils
 rabbitmq-server-3.8.9
 rh-haproxy18

docs/home/howto/BACKUP.md

@@ -51,6 +51,29 @@ epicli backup -f backup.yml -b build_folder
 
 If backup config is attached to cluster-config.yml use this file instead ``backup.yml``
 
+---
+**NOTE for Epiphany versions < 1.0.2**
+
+After releasing Epiphany v1.0.1 we found a [bug](https://github.com/epiphany-platform/epiphany/issues/2920) in the backup
+functionality. Only RHEL/CentOS based clusters with standalone (non-K8s) RabbitMQ component are affected.
+
+To work around this issue, install `python3` package (by yourself) on the first host of the `rabbitmq` group from your
+Ansible inventory file **before** running `epicli backup` command.
+
+Alternatively, if you're fine with excluding RabbitMQ from the automated backup, you can just set in your config file:
+
+```
+kind: configuration/backup
+...
+specification:
+  components:
+    rabbitmq:
+      enabled: false
+...
+```
+
+---
+
 ## 2. How to store backup
 
 Backup location is defined in ``backup`` role as ``backup_destination_host`` and ``backup_destination_dir``.