docs: add more details on rich container

[allencloud]

Signed-off-by: Allen Sun [email protected]

Ⅰ. Describe what this PR did

This pr tries to add a graph to explicitly show the architecture of rich container. And some illustration of rich container as well.

Ⅱ. Does this pull request fix one issue?

none

Ⅲ. Describe how you did it

none

Ⅳ. Describe how to verify it

none

Ⅴ. Special notes for reviews

none

[codecov-io]

Codecov Report

Merging #1440 into master will increase coverage by 22.52%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #1440       +/-   ##
===========================================
+ Coverage   16.26%   38.79%   +22.52%     
===========================================
  Files         206      256       +50     
  Lines       13759    16808     +3049     
===========================================
+ Hits         2238     6520     +4282     
+ Misses      11365     9459     -1906     
- Partials      156      829      +673

Impacted Files	Coverage Δ
daemon/logger/logmessage.go	100% <0%> (ø)
apis/metrics/metrics.go	100% <0%> (ø)
storage/volume/driver/remote.go	75.4% <0%> (ø)
storage/volume/core_util.go	19.73% <0%> (ø)
storage/volume/core.go	37.13% <0%> (ø)
cri/stream/remotecommand/errors.go	0% <0%> (ø)
storage/quota/grpquota.go	0% <0%> (ø)
storage/quota/prjquota.go	0% <0%> (ø)
pkg/serializer/serialize.go	9.52% <0%> (ø)
cri/stream/httpstream/spdy/upgrade.go	0% <0%> (ø)
... and 113 more

[houstar]

See the Section [Using systemd or sbin-init]

pouch run -d -v /tmp:/tmp --privileged --rich --rich-mode systemd --initscript /tmp/1.sh registry.hub.docker.com/library/centos:latest sleep 10000

1. I don't know that why we need --initscript here ? I think systemd is the init application that integrated in the CentOS and is enough to startup the rich container.
   i.e. We only need to --rich systemd to start the rich container.

2. From this User Case, you also specified -v /tmp:/tmp,
   I have question that If there're content in the container image's /tmp and /run , how did you handle this case ?

3. If we're running Systemd inside pouch ( so-called rich container), did we support pouch stop [container_id] has the same process as 'systemctl stop' inside pouch?

Thanks for your reply since I'm going to launch rich container to support our traditional software that using systemd.

[allencloud]

Thanks a lot for your feedback. I will try to answer your question. While feel free to share more information if there is something missing in our docs. @houstar

I don't know that why we need --initscript here ? I think systemd is the init application that integrated in the CentOS and is enough to startup the rich container.
i.e. We only need to --rich systemd to start the rich container.

--initscript is used to add a prestart hook in the container which will be executed before the systemd starts. --rich is used to choose one type of the rich container mode from systemd, dumbint.

From this User Case, you also specified -v /tmp:/tmp,
I have question that If there're content in the container image's /tmp and /run , how did you handle this case ?

This will handle it like the docker way. In most cases, it will override the inner container path.

If we're running Systemd inside pouch ( so-called rich container), did we support pouch stop [container_id] has the same process as 'systemctl stop' inside pouch

I do not think rich container will do the systemctl stop, since in the original way, pouchd would send a terminal signal to the pid=1 process in the rich container which is systemd.

[houstar]

In reply to @allencloud ,

--initscript` is used to add a prestart hook in the container which will be executed before the systemd starts. --rich is used to choose one type of the rich container mode from systemd, dumbint.

I'd like to --initscript is invisible to user and pre-defined the hook within /usr/libexec/pouch/hook.d directory. This pre-defined hook will be executed if the CMD is either systemd/init or dumbinit

From this User Case, you also specified -v /tmp:/tmp,
I have question that If there're content in the container image's /tmp and /run , how did you handle this case ?

This will handle it like the docker way. In most cases, it will override the inner container path.

If there're contents in container images's /tmp and not specified -v /tmp:/tmp, did we'll move container images's /tmp content into temporary directory and then mount tmpfs in /tmp, lastly move back the content from temporary dirtectoy to /tmp ?

I do not think rich container will do the systemctl stop, since in the original way, pouchd would send a terminal signal to the pid=1 process in the rich container which is systemd.

There're some applications needs to be gracefully shutdown. e.g. The Storage App.
I mentioned this since there're argues between Systemd and Docker.
See Systemd vs. Docker

[allencloud]

There're some applications needs to be gracefully shutdown. e.g. The Storage App.
I mentioned this since there're argues between Systemd and Docker.

I have to say systemd has no this functionality to pass the SIGTERM to its sub processes. While what I wanna say is that dumb-init supports this. @houstar

[Letty5411]

operation system -> operating system ?

[allencloud]

Thanks. Updated. PTAL @Letty5411

[Letty5411]

LGTM