Workshop Exercise - Check if Conversion Undone
Table of Contents
Objectives
- Validate that all changes and impacts caused by the conversion are undone after rolling back
- Revisit the topic of snapshot scope
- Consider next steps after rolling back
Guide
In the previous exercise, we rolled back our three tier application servers. Now we will take a closer look at where that has left us and consider next steps.
Step 1 - Our State After Rolling Back
In this step, we will repeat the observations we made on our host after the conversion with the expectation that everything is back as it was before the conversion.
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In the previous exercise, we checked that the CentOS version is reverted back. You can verify this at a shell prompt using commands like
cat /etc/redhat-releaseanduname -rto output the OS release information and kernel version. You can also refresh the Web Console to confirm the CentOS version shown on the system overview page. -
If you inflicted some damage to any of the three tier application servers with the optional Simulate conversion failure exercise, you will now find no evidence of that. You could switch over to the Ansible Automation Platform UI and run the
CONVERT2RHEL / 99 - Three Tier App smoke testjob template to verify complete application stack functionality. Or check via some of the following:For example, did you delete everything with the
rm -rf /*command or remove the standard C library with therpm -e --nodeps glibccommand? Your efforts to nuke the OS have been nullified!Did you break your three tier application by removing the PostgreSQL package on node6? If you check now with the
yum list 'postgresql*'command, you will see that postgresql packages are installed.If you filled up your disk, check now with the
df -h /command. You will see there is now plenty of free space reported.Look for any app data you added or modified after the conversion and you will find that all those changes are lost. What does this tell us about the snapshot scope implemented by our rollback playbook?
Business units will not be happy about loss of data, so make sure to raise awareness of the risk to application data when “everything scope” snapshots are employed.
Step 2 - What’s Next?
No matter what the reason is for rolling back, the next step will be to decide what to do next.
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Maybe you rolled back because there was a failure with the Convert2RHEL conversion itself or some custom automation meant to deal with your standard tools and agents. If so, assess what happened and use the experience to improve your automation to prevent similar issues going forward.
Developing robust automation is an iterative process. Remember, it’s good to fail fast! Failed conversions early in the development of your automation should be accepted as a possibility. Analysis of these issues will inform you about what adjustments need to be implemented along the way. Having an automated rollback capability helps accelerate the development of robust playbooks.
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What if you rolled back because application impact was discovered after the conversion. In this case, it’s important for the app team to investigate the cause of the impact. Once the cause is understood, roll back so what was learned can be applied to avoid the issue for subsequent conversions.
Understanding the cause of application impacts is also an iterative process. App teams must take the time required to fully assess any application issues when upgrading their dev and test servers, rolling back as often as needed. Use the lower environments in this manner so full preparations can be made before moving to production.
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After rolling back, the last pre-conversion report generated before the conversion will still be available. If no significant changes are made after rolling back, it is not necessary to generate a fresh pre-conversion report before implementing any new/additional automation and trying another conversion.
Conclusion
In this exercise section, we reviewed the state of our three tier application servers after rolling back and we considered next steps for some different scenarios.
In the next and final section of the exercise, we’ll review what we learned and explore some additional things you may want to play with in the workshop lab environment.
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