Set up a Data Guard observer on Google Cloud Compute Engine

Depending on your high availability requirements. you might want to automate failover between databases. After you've validated your Data Guard deployment, you have the option to set up a Data Guard observer on Compute Engine to do this. An observer is a process that monitors a Data Guard configuration to initiate an automated failover if conditions warrant it.

This guide covers installing the Oracle 19c database client on an observer virtual machine (VM) and configuring Fast-Start Failover.

The following examples are used throughout this guide:

Database unique name	Server hostnames	RAC instance names	Role
`DBDG_SITE1`	`site1db1`, `site1db2`	`DBDG_SITE11`, `DBDG_SITE12`	Primary
`DBDG_SITE2`	`site2db1`, `site2db2`	`DBDG_SITE21`, `DBDG_SITE22`	Standby

Install the Oracle Database client software

Create a virtual machine (VM) on Compute Engine that meets the following criteria:
- Operating system. Red Hat Enterprise Linux 7.
- Networking. A subnet with firewall rules that allow access from your Virtual Private Cloud to the Bare Metal Solution hosts running the primary and standby databases.
- Storage. -- At least 20 GB allocated to the boot disk.

host DBDG_SITE1_SCAN_HOSTNAME
host DBDG_SITE2_SCAN_HOSTNAME

If the hostnames don't resolve, add the IP addresses for each SCAN hostname to the /etc/hosts file on the VM. Replace the example IP addresses with the IP addresses for each cluster:

# Site 1 SCAN Hosts
192.0.2.10 DBDG_SITE1_SCAN_HOSTNAME
192.0.2.11 DBDG_SITE1_SCAN_HOSTNAME
192.0.2.12 DBDG_SITE1_SCAN_HOSTNAME

# Site 2 SCAN Hosts
198.51.100.10 DBDG_SITE2_SCAN_HOSTNAME
198.51.100.11 DBDG_SITE2_SCAN_HOSTNAME
198.51.100.12 DBDG_SITE2_SCAN_HOSTNAME

Install the Oracle Database RPM. Install only the software. There's no need to configure a database on the observer VM.
The Oracle Database RPM installs software in a predefined directory. Add the following entries to /home/oracle/.bash_profile to add the Oracle software home to the path:
```
cat >> /home/oracle/.bash_profile << EOL
export ORACLE_HOME=/opt/oracle/product/19c/dbhome_1
export PATH=\$PATH:\$ORACLE_HOME/bin
EOL
```
Source the Oracle environment variables in your terminal session:
```
source ~/.bash_profile
```

Configure the database connectivity

Configure the Oracle Net settings in the $ORACLE_HOME/network/admin/tsnames.ora file:

DBDG_SITE1 =
  (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = DBDG_SITE1_SCAN_HOSTNAME)(PORT = 1521))
      (CONNECT_DATA =
          (SERVER = DEDICATED)
          (SERVICE_NAME = DBDG_SITE1) (UR=A)
      )
  )

DBDG_SITE2 =
  (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = DBDG_SITE2_SCAN_HOSTNAME)(PORT = 1521))
      (CONNECT_DATA =
          (SERVER = DEDICATED)
          (SERVICE_NAME = DBDG_SITE2) (UR=A)
      )
  )

Oracle Database version 12.2 and higher includes support for the observer to run in background mode. To do so, a wallet must be created to perform passwordless authentication to the database. Log in as the oracle user on the observer VM and perform the following tasks to create a wallet:
1. Add the following entries to $ORACLE_HOME/network/admin/sqlnet.ora:
```
WALLET_LOCATION =
   (SOURCE =
      (METHOD = FILE)
      (METHOD_DATA = (DIRECTORY = /home/oracle/wallet))
)
SQLNET.WALLET_OVERRIDE = TRUE
```
2. Create the wallet directory on the VM hosting the observer:
```
mkdir /home/oracle/wallet
```
3. Initialize the wallet, then supply a password for the wallet when prompted:
```
mkstore -wrl /home/oracle/wallet -create
```
4. Create an entry in the wallet for each database in the Data Guard configuration. The mkstore command will request the SYS password for the database, followed by the wallet password provided in the previous step:
```
mkstore -wrl /home/oracle/wallet -createCredential DBDG_SITE1 sys
mkstore -wrl /home/oracle/wallet -createCredential DBDG_SITE2 sys
```
5. Confirm that the wallet contains credentials for each database in the Data Guard configuration. The -listCredential argument for mkstore will request the wallet password:
```
mkstore -wrl /home/oracle/wallet -listCredential
```
Log in to the observer VM as Oracle and then test connectivity to the primary and standby databases. Connect to the primary and secondary databases with SQL*Plus by using the wallet credentials:
```
sqlplus /@DBDG_SITE1 as sysdba
sqlplus /@DBDG_SITE2 as sysdba
```
If the wallet configuration is successful, the sqlplus command directly logs in to the database without asking for a password.

Configure and enable Fast-Start Failover

Create a directory to store the observer configuration and log files:
```
mkdir /home/oracle/fsfo
```
Connect to the Data Guard broker on the primary database using the wallet:
```
dgmgrl
CONNECT /@DBDG_SITE1;
```
View the Data Guard status to check that the configuration is marked as SUCCESS:
```
SHOW CONFIGURATION;
```
Enable Fast-Start Failover (FSFO):
```
ENABLE FAST_START FAILOVER;
```
Enabling FSFO does not make the configuration ready for automatic failover. Automatic failover requires an observer.

Start Data Guard Observer:

START OBSERVER observer1 IN BACKGROUND FILE IS '/home/oracle/fsfo/observer1_DBDG.dat' LOGFILE IS '/home/oracle/fsfo/observer1_DBDG.log';

In a separate terminal session, verify the configuration:

SHOW CONFIGURATION VERBOSE;

The following example shows the verbose mode of the show configuration command. If the configuration status is SUCCESS, your setup is complete.

Configuration - DBDG

  Protection Mode: MaxAvailability
  Members:
 DBDG_SITE1 - Primary database
   DBDG_SITE2 - Physical standby database

  (*) Fast-Start Failover target

  Properties:
    FastStartFailoverThreshold      = '30'
    OperationTimeout                = '30'
    TraceLevel                      = 'USER'
    FastStartFailoverLagLimit       = '45'
    CommunicationTimeout            = '180'
    ObserverReconnect               = '0'
    FastStartFailoverAutoReinstate  = 'TRUE'
    FastStartFailoverPmyShutdown    = 'TRUE'
    BystandersFollowRoleChange      = 'ALL'
    ObserverOverride                = 'FALSE'
    ExternalDestination1            = ''
    ExternalDestination2            = ''
    PrimaryLostWriteAction          = 'CONTINUE'
    ConfigurationWideServiceName    = 'DBDG_CFG'

Fast-Start Failover: Enabled in Potential Data Loss Mode
  Lag Limit:          45 seconds
  Threshold:          30 seconds
  Active Target:      DBDG_SITE2
  Potential Targets:  "DBDG_SITE2"
    DBDG_SITE2   valid
  Observer:           observer1
  Shutdown Primary:   TRUE
  Auto-reinstate:     TRUE
  Observer Reconnect: (none)
  Observer Override:  FALSE

Configuration Status:
SUCCESS