Optimize LoadBalancer Application Availability

High Availability (HA) is key to keeping applications and databases available in the event of a system failure or load spike. For this reason, the use of Load Balancer (LB) Applications is critical in HA architectures to distribute traffic to various database servers. Optimize LoadBalancer Application Availability by ensuring even distribution to avoid overloading at a single point. In this way, HA ensures that the application continues to run at optimal performance even when there is an outage on one or more nodes. Load Balancers (LBs) serve as a key component to evenly distribute connections to available database servers, maintaining the availability of critical applications and data.

Best Practices

1. Load Balancer Setup:
   • Load Balancer Type: Use a load balancer that supports the distribution of traffic to the database with algorithms such as round-robin, least-connections, or IP hashes. Examples: HAProxy, NGINX, or AWS ELB.
   • Health Checks: Implement health checks on load balancers to monitor the health status of database nodes. If a node fails, the load balancer should automatically redirect traffic to healthy nodes.
2. Database Replication:
   • Master-Slave Replication: Configure master-slave replication where the master receives all write operations and the slave is used for read operations. This can reduce the load on the master server and increase HA.
   • Multi-Master Replication: For systems that require high write availability in multiple locations, multi-master replication may be considered. Make sure to handle conflicts effectively.
3. Automatic Failover:
   • Failover Mechanism: Use tools like Pacemaker or Patroni to detect failures on the primary database server and automatically failover to the secondary node without manual intervention.
   • DNS-based Failover: Use DNS-based failover to redirect traffic to another data center or region if the entire infrastructure goes down.
4. Data Consistency & Split-Brain Scenarios:
   • Quorum-based Systems: In a multi-node configuration, ensure that the system has a quorum mechanism in place to prevent split-brain scenarios, where two independent nodes consider themselves masters.

Using Oracle Connection Manager

Langkah 1: Instalasi Oracle Connection Manager

Oracle Connection Manager (CMAN) is a proxy server that can be used to distribute client connections to Oracle databases.

1. CMAN Installation:Instalasi Oracle Connection Manager dilakukan melalui Oracle Universal Installer (OUI) yang tersedia dalam instalasi Oracle Database Client.
2. Connection Manager Configuration:After installation, the configuration file cman.ora which is usually in $ORACLE_HOME/network/admin/cman.ora.

Step 2: Using CMAN as a Load Balancer

On clients accessing the database, use the following configuration on the tnsnames.ora

#2. Database Replication: Master-Slave Setup

Oracle provides the Data Guard feature for Master-Slave Replication implementations, which provides data replication from the primary database to the backup database.

Step 1: Configure the Primary Database

1. Enable Force Logging:To ensure all changes are logged in the redo logs.ALTER DATABASE FORCE LOGGING;
2. Enable Archivelog Mode:Make sure the database is running in archivelog mode.SHUTDOWN IMMEDIATE; STARTUP MOUNT; ALTER DATABASE ARCHIVELOG; ALTER DATABASE OPEN;
3. Create Standby Redo Logs:Standby redo logs are required for Data Guard configuration.ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/orcl/stdby01.log') SIZE 500M;
4. Create a TNS Entry for Standby:Add entries to the tnsnames.ora on the primary server that leads to standby.STDBY = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.11)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = orcl_stdby) ) )
5. Backup Primary Database and Send to Standby:Use RMAN to create backups and send them to standby.
   RMAN> BACKUP DATABASE PLUS ARCHIVELOG;
   Then restore on standby.

Step 2: Configure Database Standby

1. Restore Backup on Standby: Restore Backup on Standby:RMAN> RESTORE DATABASE; RMAN> RECOVER DATABASE;
2. Start Standby Database: Start the database in standby mode.ALTER DATABASE MOUNT STANDBY DATABASE;
3. Enable Managed Recovery: Enable managed recovery for standby.ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;

#Conclusion

• Load Balancer: Use Oracle Connection Manager to distribute the connection load evenly among database nodes.
• Master-Slave Replication: Use Oracle Data Guard to ensure real-time replication of data from primary to standby database.
• Multi-Master Replication: Using Oracle GoldenGate to implement bi-directional replication between multiple database masters, allowing each node to perform write operations and stay in sync with other nodes.
• Automatic Failover: Pacemaker and Corosync along with Oracle Data Guard provide an automated failover mechanism that can be installed in a self-managed VPS environment.
• DNS-based Failover: Bind9 can be used to manage DNS failover automatically by redirecting traffic to the standby node when the primary node fails.
• Data Consistency & Split-Brain Scenarios: Quorum-based systems configurations with STONITH protect databases from split-brains, maintaining data consistency across clusters.

With this configuration, your Oracle database system will have High Availability and Protection against various failure scenarios without using external cloud services.