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Availability
How to get your system uptime to the maximum.
NGA - High Availability Configuration (HAC)
This chapter provides an overview of the High Availability Configuration for redundant or non-redundant WinCC OA projects (High Availability Configuration - HAC) and explains the roles of the components etcd and Patroni, which are required to set up HAC.
Installation and Configuration - Windows
This chapter provides an overview of the installation and configuration steps for the High Availability Configuration (HAC).
Step 4 – WinCC OA Configuration
Create the WinCC OA schema in the PostgreSQL® database on the Patroni leader node. Then, create a WinCC OA project using NGA and set up the database connections.

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- Redundancy
  The high availability requirements of plant constructors and operators as well as the process and data security can be covered with the redundancy concept of WinCC OA.
- Redundant network connections
  In order to achieve a better fault tolerance WinCC OA Managers can connect to other WinCC OA Managers running on different computers via redundant network connections (this means connecting through two network connections (= IP connection)).
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  The alive mechanism in WinCC OA serves for connection controlling between the single managers. Each manager sends alive messages at definable intervals.
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  The identification caching provides you an advantage especially when using remote user interfaces and distributed systems. Identification caching allows the identification to be sent as “delta” instead of the whole identification. Thus, only the changes are sent by the Data and the Dist managers.
- System Dashboard
  The System Dashboard in WinCC OA provides a central overview of system status, performance metrics, and security aspects. It helps operators and administrators quickly view and assess important information.
- NGA - High Availability Configuration (HAC)
  This chapter provides an overview of the High Availability Configuration for redundant or non-redundant WinCC OA projects (High Availability Configuration - HAC) and explains the roles of the components etcd and Patroni, which are required to set up HAC.
  - Requirements
    This chapter contains the requirements for NGA - High Availability Configuration (HAC).
  - Installation and Configuration - Windows
    This chapter provides an overview of the installation and configuration steps for the High Availability Configuration (HAC).
    - Step 1 – Installation of necessary Software
      In this step, you set up the environment for WinCC OA and PowerShell 7 on both server and database machines. You install PowerShell 7, extract the Environment Setup (PES), and install Python, , and . The PES package provides the supported version, configuration templates, and database schema scripts. After installation, you configure the 'pes' user, set permissions, and apply firewall rules to complete the high-availability cluster setup.
    - Step 2 – Configuration of the etcd Cluster
      In this step, you configure and start the service on database server 1, database server 2, and the dedicated etcd server to enable high availability. You configure and start the etcd service on each etcd server. Afterwards, you verify the cluster state by storing and retrieving a test key-value pair and checking the status of all nodes using etcdctl commands.
    - Step 3 – Configuration of the Patroni Cluster
      Set up the Patroni cluster with the provided configuration file template and the PostgreSQL® binaries from the WinCC OA installation. Adapt the configuration to your project needs. For example, calculate and configure the disk space for WAL retention to enable fast recovery after a node failure.
    - Step 4 – WinCC OA Configuration
      Create the WinCC OA schema in the PostgreSQL® database on the Patroni leader node. Then, create a WinCC OA project using NGA and set up the database connections.
  - Installation and Configuration - Linux
    This chapter provides an overview of the installation and configuration steps for the High Availability Configuration (HAC).
  - Failover and Recovery Scenarios
    This chapter explains the failover and recovery scenarios for the High Availability Configuration (HAC).
  - Update Scenarios
    This chapter describes the update scenarios for the High Availability Configuration (HAC).
  - Restrictions
    This chapter contains the restrictions for NGA - High Availability Configuration (HAC).
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Step 4 – WinCC OA Configuration

Create the WinCC OA schema in the PostgreSQL® database on the Patroni leader node. Then, create a WinCC OA project using NGA and set up the database connections.

1. Create the WinCC OA Schema in the PostgreSQL® Database

On the Leader node of Patroni, which serves as the primary PostgreSQL® database, test the connection by running:
```
<WinCC OA installation>\bin\pgsql\bin\psql.exe -U postgres
```

After confirming the connection, create the WinCC OA schema by executing the following command:

<WinCC OA installation>\bin\pgsql\bin\psql.exe -f <WinCC OA installation>\data\NGA\PostgreSQL\sql\schema.sql -U postgres

2. Create the WinCC OA Project

Depending on your requirements, create a redundant or a non-redundant WinCC OA project using NGA with the Manual configuration option (for Manual configuration see chapter Archiving). This means that a managed PostgreSQL® database will not be created automatically.
Configure the Database Connection for both the PostgreSQL® backend and the PostgreSQL_2 backend as follows:
```
<IP of Database Server 1>:5432$<IP of Database Server 2>:5432
```
In a redundant network configuration, you can change the database connection by specifying
```
<IP of Database Server 1>,<2nd IP of Database Server 1>:5432$<IP of Database Server 2>,<2nd IP of Database Server 2>:5432
```