Re: Reproducibility of builds

[Claudius Heine <claudius.heine.ext@siemens.com>]

Hi,

On 08/21/2017 01:23 PM, [ext] Claudius Heine wrote:
> Hi,
> 
> On 08/03/2017 10:13 AM, Claudius Heine wrote:
>> Hi,
>>
>> am I right that Isar supports or should support reproducible root file 
>> system build?
>>
>> If I understand correctly, when multistrap is called, it fetches 
>> always the latest version of all packages from the debian repository 
>> mirrors. Am I mistaken or is this feature still on the roadmap?
>>
>> I that is on the roadmap, how are you thinking of solving this issue?
>>
>> The openembedded way would be to seperate the fetch and 'install' step 
>> and first download all packages into the DL_DIR and then use them from 
>> there. Maybe we could create this pipeline:
>>
>> dpkg-binary Recipe:
>>
>> fetch deb file into downloads -> insert into local repository
>>
>> dpkg-source Recipe:
>>
>> fetch sources into downloads -> build packages -> insert into local 
>> repository
>>
>> image Recipe:
>>
>> fetch all required packages into downloads -> insert all of them into 
>> the local repository -> create root fs using only the local repository
>>
>> Multistrap provides a '--source-dir DIR' parameter, that stores all 
>> installed packages into a directory. So if we would use that as a 
>> fetcher, then we would create a temporary rootfs just to get all 
>> required packages for the project.
>>
>> Are there other possible solutions for this?
> 
> The problem with this solution is that its not possible to create 
> multiple images with different sets of packages that share the version 
> of the all the common packages.
> 
> An alternative solution is to employ a repository cacher that caches the 
> 'Packages.gz' of the first request. This way it would also be faster 
> then running multistrap one additional time just to fetch all required 
> packages.
> 
> Maybe apt-cacher-ng or something similar can be used for this.
> However I am currently not sure how this can be integrated into the 
> current build process. Some ideas? Maybe implementing a simple repo 
> caching proxy that is integrated into isar?
> 
> The repository cacher is likely a daemon running in parallel to 
> multistrap and fetches everything to the DL_DIR that is requested by it. 
> Maybe provide a 'clean_package_cache' task, that deletes the cached 
> 'Packages.gz', causing the next root fs build to use new package versions.
> 
> I would really like to hear some feedback on this.

In our meeting today, it was discussed that we should collect all 
requirements for this feature and discuss possible implementation ideas 
based on those requirements.

Here are some requirements from my side:

     1 If multiple different images with some common set of packages are
       build with one bitbake call, then all images should contain
       exactly the same version of every package that it has in common
       with any of the other images.

     2 The resulting image should only depend on the build environment
       and isar metadata, not on the point in time it is build.
       This means if the environment, including the downloads directory,
       is complete (for instance by an earlier build of the image), every
       following build of this image recipe should result in exactly the
       same packages installed on this image.

     3 Binary and source packages should be part of the archival process.
       Source packages are useful in case some package needs to be
       patched at a later date. Binary packages are useful, because
       building them from source packages is currently not 100%
       reproducible in Debian upstream. [1]

     4 For development, it should be possible to easily reset the
       environment, triggering an upgrade of the packages on the next
       image build.

     5 Deployable in CI environments. What those are exactly should be
       further discussed. Here are some:

       5.1 Possibility to use a download cache, that is not bound to only
           one product/image/environment

       5.2 More than one build at the same time in one environment should
           be possible

     6 Efficiency: The reproducibility feature should be time and
       resource efficient as possible. E.g. Process should only fetch and
       store the required files.

     7 Outputs a description file with the name and version of every
       package deployed/used in the image/environment.

To 5: Since I don't have much experience with CI systems, requirements 
mentioned here might not be correct.

Any comment or requirement additions are welcome.

Cheers,
Claudius

[1] https://tests.reproducible-builds.org/debian/reproducible.html

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