thank you for sharing your experiences, that was helpful
On Saturday, December 12, 2020 at 7:47:50 PM UTC+1 [email protected] 
wrote:

> El lunes, 7 de diciembre de 2020 a las 16:12:10 UTC+1, [email protected] 
> escribió:
>
>>
>> Hi!
>>
>> I am using Jenkins in Docker and I map a folder from local machine to the 
>> container's /var/jenkins_home to preserve JENKINS_HOME.
>>
>> There are two things I am wondering about, and maybe you can comment:
>>
>> 1. Can new Jenkins corrupt existing JENKINS_HOME?
>> Let's assume I have Jenkins in version X running, I want to upgrade so I 
>> have built new image, with Jenkins version Y, same plugins - maybe updated 
>> during the image build
>>
>> Is it possible that when I restart Jenkins with new image with version Y, 
>> the existing JENKINS_HOME won't be compatible with new version? 
>> Is it possible that after restart JENKINS_HOME will be changed in a way 
>> that it won't be possible to use it again with version X - if I want to 
>> rollback for whatever reason?
>>
>>
> It depends of your plugins installed, so it is possible you screw up your 
> Jenkins Home if you do not test your upgrade in a test instance, it is not 
> common but it could happens, thus is recommended to clone your Jenkins home 
> folder and test the upgrade before to make it on production. Also, take a 
> backup before to make the upgrade is mandatory. Rollback is not 
> supported, even though it could work, it is better to restore the backup 
> form the previous version.
>  
>
>> 2. What happens when two instances share JENKINS_HOME?
>> I want to have a simple test environment - let's not discuss now if it's 
>> a good or bad approach :) - so next to a working Jenkins container I start 
>> another one in a quiet mode (no job will start), with a new image I want to 
>> try out
>> The first idea is to copy original JENKINS_HOME and use this copy, but 
>> what if the home is very big and I do not have much space - how bad would 
>> running second Jenkins with JENKINS_HOME mapped to the same folder on a 
>> local host would be? (I haven't considered that option, but I was asked 
>> 'why')
>>
>> I know I can just run it and check, but I think there might be plenty of 
>> different cases that I will not see in my simple test, but maybe some of 
>> you have more experience or ran into issues before
>>
>>
> Really bad idea, Jenkins keep changes in memory and write them to disk, so 
> if you have two instances running in the same Jenkins home and you change a 
> job in one of them the other does not know anything about his change, the 
> configuration is not read from disk on runtime, most of the configuration 
> is only read at start time and keep updated in memory. So two instances 
> running on the same Jenkins home is a random behaviour environment.
>
>  
>
>> BR
>> Ewelina
>>
>

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