Hi Waldek,
so what you'd like to achieve is to run cpiod only on first run, then run
the actual bootcmd on all subsequent runs.
I find such behaviour useful and would be very happy if we could do it in a
way that would work for cloud-init
as well.
I was thinking, could we perhaps modify cpiod so that it would exit
immediately if there was some specific file present on
the unikernel's filesystem (e.g. /cpiod-skip)? In other words, the command
would then look like this:
- '/tools/cpiod.so --prefix / --conditional; runscript/the_config'
When the "--conditional" flag is used and "/cpiod-skip" is present, then
the first part ("'/tools/cpiod.so --prefix / --conditional") would return
immediately. And the bootcmd would effectively become only
"runscript/the_config".
All we need to do then is to make sure the file "/cpiod-skip" is uploaded
during the "capstan package compose-remote".
Such approach would also work with cloud-init even if all commands there
are always run.
What do you think?
Dne ponedeljek, 06. november 2017 06.23.30 UTC+1 je oseba Waldek Kozaczuk
napisala:
>
> In last couple of weeks I have been working with MikelAngelo capstan team
> to add a feature 'compose-remote' that allows composing and uploading files
> to a remote OSv instance with cpiod running.
>
> This feature is aimed to help speed-up creation of OSv AWS immutable amis
> which right now is extremely slow if one wants to import pre-baked OSv raw
> image as a snapshot and create an AMI of it. The new idea is that every
> time user wanted to create final application AMI he/she would create a
> bootstrap or 'base" AMI (cmdline=''/tools/cpiod.so --prefix /") in a
> traditional way, start EC2 instance with running cpiod, upload extra files
> using capstan and take a snapshot and create new AMI which I tested and is
> much faster. This could be applied to all other cases where uploading to a
> remote instance makes more sense.
>
> The only remaining problem how one set new cmdline. There is a least one
> way of achieving it. One would bake in cloud-init module in a base AMI and
> have it set cmdline using httpserver and proper command in user data ec2
> start. There are many downsides - it would not work in non cloud-init
> friendly environments, cloud init is pretty heavy and complicated tool to
> achieve something so simple and depends on httpserver. Please it does not
> let me create immutable AMIs with preset cmdline.
>
> Here is my idea: create simple new tool - setcmdline.so that would behave
> like so:
>
> - set new cmdline if it is passed non-empty explicit cmdline
> - set new cmdline from a content of file /cmdline if one present and
> delete it
> - do not change cmdline otherwise
>
> Now user would use it in one of 2 ways - set cmdline of base AMI like so:
>
> - '/tools/cpiod.so --prefix /; /tools/setcmdline.so' and have capstan
> upload a file /cmdline with appropriate content when uploading all other
> files
> - '*/tools/cpiod.so --prefix /; /tools/setcmdline.so "**runscript
> /run/the_config**"'*
>
> Another alternative I toyed with would be to enhance cpiod to handle new
> 'setcmdline' command but it seems pretty hackish and also requires
> modification of capstan.
>
> What do you think?
> Waldek
>
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