Manuel des bonnes pratiques > Environnement à deux systèmes - Zéro Downtime

Two-Installation Environment

Setting up a two-installation environment for the Zero Downtime Upgrade is the best practice in order to have a base and a target installation ready to upgrade and test properly.

Notes

The ZDU is available as of v11.2 of the Automation Engine, therefore the following instructions refer to that version as lowest possible base version.

In the documents pertaining to the ZDU, all references to base and target installation also mean base and target version.

Two special modes exist for this upgrade function, the compatibility mode and the parallel mode.
Compatibility mode: This mode is started as soon as you choose the option BEGIN from the ZDU wizard.
In this mode, which is in effect until you choose the option FINALIZE, certain system optimization functions are not available. Also system performance will be reduced noticeably.
Parallel mode: A mode during the upgrade when base and target version processes are active at the same time.

Whenever you upgrade your system, Automic strongly recommends using a test system for extensive testing before installing upgrades on your production system.

General

In order to be able to seamlessly upgrade the Automation Engine without any downtime, using the Zero Downtime Upgrade function, you have to set up two separate installations.
They serve to ensure that a base and target version are available for conducting the upgrade and testing the proper running of tasks and jobs in the target version.
As base and target version CPs/WPs will be active during the parallel mode, you have to set up two separate installations in separate bin directories.

Initially both installations will be the same. In the course of the upgrade one of them will be upgraded to the target version, whereas the other (base) installation will subsequently be shut down, as soon as all processes and tasks run satisfactorily in the target version.

These may be two installations on:

the same host (recommended)
two separate hosts

You can use 1. or 2. with a Proxy, details you find below.

The two alternatives can be realized using either two (new) AE installations or an existing AE installation, by duplicating it.

I. Two-Installation Environment - Two Separate Installations

Set up two installations of the AE system you want to upgrade from (v11.2 or higher).
1. Use either the same host and set up two separate installations.
2. Alternatively use two separate hosts and separate installations.
The installation that will be used as target version needs to be set up with the Automation Engine directory and Utility directory only. Those are needed for upgrading.
The INI and configuration files of these two core components in the target version installation have to contain the same configuration information as the ones in the base version installation.
You also have to configure double the amount of ports than are usually necessary for the correct working of an AE system.
1. These ports have to be known to any clients that are going to connect to a CP, therefore enter them either in the INI or the configuration files.
  This is necessary, because at some point during the upgrade base and target version CPs have to be active in the parallel mode at the same time.
Start the ZDU by starting the base version installation and the ZDU there.

Advantages:

Using this kind of setup lets users continue their work without being disconnected.
Agents can be phased out successively and connect to the new CPs.

Disadvantages:

Setting up the system this way requires a little more preparation time at first.
Additional ports are necessary, which have to be configured in Firewall and existing Proxies.
All ports have to be known by all existing clients before you start the upgrade.

II. Two-Installation Environment - Duplicate an Existing Installation

You will reuse the files of an existing AE installation, following these steps:

You have to use two separate bin directories, in which the INI and configuration files of the Automation Enginebin directory and the Utilities bin directory will be contained.
Create a bin directory for the contents of the Automation Engine folder and the Utilities folder, respectively, in a location of your choice.
Copy and paste all files from those two folders in the existing installation to the respective folders in the new location.
This second location and the new folders there represent the target version installation for the ZDU process.
Start the original installation and start the ZDU.

Advantage:

Less time needed for configuring ports, as no additional ports are necessary.

Disadvantages:

Shutting down CPs results in agents and users connected to those CPs being disconnected.
System performance will be reduced to half of its usual amount.

III. Combine with a Proxy

You can execute the ZDU by using the most hassle-free solution and run a Proxy.

The Proxy combines and reroutes CP connections, while agents just connect to the Proxy, using the ports or port ranges configured in it.

You have to set up one of the installation variants explained above, use a two-installation setup or duplicate your existing installation.
Configure the second installation in the Proxy accordingly.
The Proxy will then reroute connections to either the base or target version CPs, as necessary.

Advantages:

You do not have to configure any additional ports, either in the two-system environment or the split system environment.
The connections will be taken care of by the Proxy so that agents will be connected to whatever system and CPs are active and in use, be it base or target system.

Illustration 1: Proxy-based two-system environment solution