Farewell to ClickOps: OCI CLI seamless Data Guard Replication for ExaC@C

Intro

Since the very beginning, everyone got introduced to  Cloud services through the console as it’s very quick. But the cloud CLI tooling provides a stronger, yet user-friendly way to automate tasks, often covering features not even available in the console. Moreover, DBAs often assume that the CLI is primarily designed for managing compute-based services, overlooking its potential benefits for their database fleet. In this tutorial, we’ll demonstrate how to automate the Data Guard association of your database between two Exadata Cloud at Customer infrastructures in separate regions.
On top of it, I’ll show you where to look and the type of logs that are generated if you need to troubleshoot.

Using the API to Enable Data Guard on ExaC@C

REST API Endpoint
Obviously, Rest APIs provided by the Cloud platform is the core vehicle that allows anything (infrastructure resource, or cloud services) to be created, deleted or managed.
This why the best thing to explore a new feature is to check the REST API Endpoint. In our case the endpoint is
CreateDataGuardAssociation

$ oci db data-guard-association create from-existing-vm-cluster [OPTIONS]

You can check more details here CreateDataGuardAssociationDetails

API method for a Data guard association using existing cluster

Below is the configuration details for creating a Data Guard association for a ExaC@C Vmcluster database

• CreateDataGuardAssociationToExistingVmClusterDetails

The attributes are as below

API request Examples

Here is a basic API call example for Database system which slightly differs from the Exadata Cloud implantation.

Response Body

The response body will contain a single DataGuardAssociation resource.

Using OCI CLI to Enable Data Guard on ExaCC

Now that we’ve explored REST API structure, we can move to a practical example using OCI CLI. Both Exada Cloud@Customer (Edge DB service) are located in different regions in Canada in 2 DataCenters.   

Usage

$ oci db data-guard-association create from-existing-vm-cluster [OPTIONS]

Generate a sample json file to be used with this command option.

The best way to leverage OCI CLI with a complex structure is to generate a full command JSON construct.

 $ oci db data-guard-association create from-existing-vm-cluster 
--generate-full-command-json-input > dg_assoc.json
{
  "databaseAdminPassword": "string",
  "databaseId": "string",
  "databaseSoftwareImageId": "string",
  "peerDbHomeId": "string",
  "peerDbUniqueName": "string",
  "peerSidPrefix": "string",
  "peerVmClusterId": "string",
  "protectionMode":"MAXIMUM_AVAILABILITY|MAXIMUM_PERFORMANCE|MAXIMUM_PROTECTION"
,"transportType": "SYNC|ASYNC|FASTSYNC" }

Practical Example

Here we will configure a Data guard setup from an ExaC@C site to another with no existing standby DB home.

• Below template matches a DG association without a peer Database Home in the standby VM Cluster

vi dg_assoc_MYCDB_nodbhome.json  

{ 
  "databaseAdminPassword": "Mypassxxxx#Z",       
  "databaseId": "ocid1.database.oc1.ca-toronto-1.xxxxx",   <--- primary DB
  "databaseSoftwareImageId": null,
  "peerDbHomeId": null,
  "peerDbUniqueName": "MYCDB_Region2",   <--- Standby DB
  "peerSidPrefix": "MYCDB",
  "peerVmClusterId": "ocid1.vmcluster.oc1.ca-toronto-1.xxxxxx", <--- DR cluster
  "protectionMode": "MAXIMUM_PERFORMANCE",
  "transportType": "ASYNC",
  "isActiveDataGuardEnabled": true    
}

• Now we can run the full command with the adjusted JSON template

oci db data-guard-association create from-existing-vm-cluster 
     --from-json  file://dg_assoc_MYCDB_nodbhome.json 

Response Body

• You will need the id to check the status (Check for SUCCESS or FAILURE)

# export workreq_id=ocid1.coreservicesworkrequest.xxxxx
# oci work-requests work-request get --work-request-id $workreq_id \
 --query data.status

Troubleshooting

Automating tasks with CLI provides the advantage of not leaving you in the dark when things go awry. Here are some valuable troubleshooting insights when using OCI CLI: 

• The work request status and error detail is easily accessible using get command for troubleshooting 

• API based operations on existing systems like DB replications, offer comprehensive logs that are invaluable for diagnosing issues inside the target servers (i.e Exadata Cloud VM clusters).

• Oracle Data Guard association ensures clean rollbacks for quick retries in case of failures – a significant advantage over manual cleanup which we all hated back in on-premises setups.

Work request

The very first thing to check is the status of the request and the details of the error in case of failure.

• Even without a work request ID, the below query allows you to list all previous data guard association jobs

# oci work-requests work-request list -c $comp_id –-query \
data[?\"operation-type\"=='Create Data Guard'].\
{status:status,operation:\"operation-type\",percent:\"percent-complete\",
\"workreq_id\":id}" --output table

• The output will look like the below .

• You want to display details about the error? Sure there is an OCI command for that 

# oci work-requests work-request-error list --work-request-id $workreq_id –all \
 --query "data[].[code,message]" --output table

• You can see few insights on the stage where your DG association failed for instance

Logs in your ExaData Cloud@Customer

When a database related operation is performed on an ExaC@C VM , log files from the operation are stored in subdirectories of /var/opt/oracle/log.
check logs
Running below find command while your Data guard association is running can help you list the modified logs

$ find $1 -type f -print0 | xargs -0 stat --format '%Y :%y %n'| sort –nr \
| cut -d: -f2- | head

PRIMARY

let’s see what logs are created on the primary side

☆ dg folder

This will likely contain below files. 

$ ls /var/opt/oracle/log/GRSP2/dbaasapi/db/dg
dbaasapi_SEND_WALLET_*.log
dbaasapi_CONFIGURE_PRIMARY_*.log
dbaasapi_NEW_DGCONFIG_*.log
dbaasapi_VERIFY_DG_PRIMARY_*.log
dbaasapi_SEND_WALLET_*.log

1. VERIFY_DG_PRIMARY
First file created is {log_dir}/<Database_Name>/dbaasapi/db/dg/dbaasapi_VERIFY_DG_PRIMARY*.log

$ tail -f dbaasapi_VERIFY_DG_PRIMARY_2022-05-27_*.log
...
Command: timeout 3 bash -c 'cat < /dev/null > /dev/tcp/clvmd01.domain.com/1521'
Exit: 124
Command has no output
ERROR: Listener port down/not reachable on node: clvmd01.domain.com:1521
...

Below excerpt shows the precheck step that failed, which was fixed by running the oci cli command again

2. PRIMARY_Configure

After the second run, the prechecks passed, but now there’s an issue with the primary configuration (se below).

Let’s dig a bit deeper , but it seems it’s related to some service not being able to start.

☆ dgcc folder

“dgcc” represents the Data Guard Configuration checker, which is responsible for checking the Data Guard status and configurations. Below logs contain information about the activities and status of dgcc on the ExaC@C

$  ls /var/opt/oracle/log/MYCDB/dgcc  
dgcc_configure-sql.log 
dgcc_configure-cmd.log
dgcc_configure.log

☆ dgdeployer folder

DGdeployer, is the process that performs the DG configuration. The dgdeployer.log file should contain the root cause of a failure to configure the primary database mentioned earlier.

$  ls /var/opt/oracle/log/MYCDB/dgdeployer
 dgdeployer.log
 dgdeployer-cmd.log

As displayed here, we can see that the PDB service failed to start

☆ dgrops folder

The dgrops  log file contains the output of the dgrops script, which includes the steps performed, the commands executed, and any errors or warnings encountered.
This log helped identifying the issue which was that the PDB state wasn’t saved in the primary CDB.

Solution

On the primary CDB, restart the PDB and save its state and voila.The DG association should now be successful.    

$ alter pluggable database MYPDB_TEST close instances=all;
$ alter pluggable database MYPDB_TEST  open instances=all;
$ alter pluggable database MYPDB_TEST  save state instances=all;

STANDBY

At this point, there are no troubleshooting steps left. But I though I’d add a list of available logs at the DR site.
☆ prep folder

This will store logs about preparation of the standby including creating the DB home based on our previous example

$ view /var/opt/oracle/log/MYCDB/prep/prep.log 

☆ dg folder

This folder will include logs pertaining to the standby database creation as shown below

$  view /var/opt/oracle/log/MYCDB/dbaasapi/db/dg/dbaasapi_CREATE_STANDBY_*.log 

Conclusion

This tutorial we learned to

• Seamlessly automate Data Guard associations between diverse ExadataCloud@Customer systems.

• leverage OCI CLI & JSON templates to discover its extensive utility beyond compute services.

• Additionally, you now have a clear understanding of where to access and how to interpret the logs, essential for troubleshooting potential issues.

• Hope this will encourage every DBA to start using OCI CLI every day for their administration tasks

Thank you for reading