Re: Droplets and Stacks

Guillaume Berche

Thanks Mike for your detailed response, more comments inline

On Tue, Aug 4, 2015 at 3:52 PM, Mike Dalessio wrote:

Just to clarify, applications intentionally do NOT require restaging to be
placed onto a new rootfs; a droplet is compatible with all future versions
of a specific rootfs.

When an operator deploys an update to CF with a new rootfs, the DEA VMs
get rolled, and all new application instances (when they come up) are
running on the new rootfs.
thanks for correcting me on that. I had in kept mind the GHOST
vulnerability into which statically linked binary in the app or buildpack
would require a restaging (cf )
but that's likely to not be that much a common case

Am I right to assume that there will be multiple distinct stack instances
returned by cc api calls such as [3] (with distinct guid but same entity
names) and that stacks are indeed immutable (i.e. the field "updated_at"
will remain null in [4] ) ? Writing a cli plugin to identify apps that need
restaging following a rootfs patch (similar to [2] but for a minor version
of a given stack), would therefore browse all stacks using [5], and order
those with the same name to understand minor patch version ?

I recall similar discussion related to buildpack versionning, where it
was mentionned that the buildpacks were mutable, and the only strategy to
support multiple versions of a buildpack is to append version numbers to
the buildpack names (and rely on priority ordering to have most recent
version be picked first). This has the drawback that an app specifying a
buildpack (e.g. to deambiguate or fix an invalid detect phase) will then
need to manually update the buildpack reference to benefit from new version
(a restaging won't be sufficient).

Is this correct ? On CF instances that don't version buildpack names, how
can users know whether apps were stage a vulrenable version of an offline
buildpack, and require restaging ? Is it by comparing staging date, and
known rootfs patch date ?
It's possible that we're conflating rootfs patches with buildpack patches.
I tried to address rootfs patches above, and so will address buildpack
patches here.

It's possible to determine the buildpack used to stage an app via the CC
API, and in fact versions of the CLI 6.8.0[7] and later will display this
information in the output of `cf app`.
The cli displays the 'detected_buildpack' or 'buildpack' field returned by
the app summary endpoint [g2] such as reproduced below

$ cf app spring-startapp
Showing health and status for app spring-startapp in [...]

requested state: stopped
last uploaded: Wed Apr 29 15:14:48 UTC 2015
stack: cflinuxfs2
buildpack: java-buildpack=v3.0-
t#3bd15e1 open-jdk-jre=1.8.0_45 spring-auto-reconfiguration=1.7.0_RELEASE
-access-logging-support=2.4.0_RELEASE tomcat-instance=8.0.21
pport=2.4.0_RELEASE tom...

I understand the detailed buildpack versionning info is the data returned
by the buildpack detect script [g3]. So buildpacks (such as javabuild pack)
that would provide detailed versionning info in the detect method would
help cf operators understand if some apps are running specific vulnerable
versions of the buildpack.

On an app which was targetting a specific buildpack (e.g. -b
java-buildpack), I understand the displayed detected buildpack would not
contain as much details, and mere display the buildpack name (or git url).
If you confirm, I'll try to send a PR for on docs-* repo related to [3] to
suggest to print out detailed versionning info for custom buildpacks
(currently suggests to display a "framework name" with "Ruby" as an

The /v2/buildpacks endpoint (used by the "cf buildpacks" command) displays
the last update date for a buildpack, e.g.

"metadata": {
"guid": "e000b78c-c898-419e-843c-2fd64175527e",
"url": "/v2/buildpacks/e000b78c-c898-419e-843c-2fd64175527e",
"created_at": "2014-04-08T22:05:34Z",
"updated_at": "2015-07-08T23:26:42Z"
"entity": {
"name": "java_buildpack",
"position": 3,
"enabled": true,
"locked": false,
"filename": ""

Would'nt it make sense to have the CC increment a version number for each
update so that it becomes easier to query than only relying on dates
comparison ?

While it's great to have buildpacks provide themselves detailed versionning
info for their code and their most important dependencies/remote artifacts,
I feel the cf platform should provide a bit more support to help identify
versions of buildpacks used by apps, such as:
- refine the app summary endpoint [g2]:
- for system buildpacks: include the buildpack guid (in addition to the
buildpack name) as to allow correlation to /v2/buildpacks endpoint
- for custom buildpacks (url): record and display the git hash commit
for a buildpack url
- refine the app listing endpoints [g4] or v3 [g5] to
- support querying app per system buildpack id
- support querying app by dates of "package_updated_at" or best a
version number as suggested above

I'm wondering whether the CAPI team working on API V3 is planning some work
in this area, and could comment the suggestions above.


However, that doesn't easily answer the question, "who's running a
vulnerable version of the nodejs interpreter?", or even harder to answer,
"who's running a vulnerable version of the bcrypt npm package?" which I
think is more along the lines of what you're asking.

Currently, there's an exploratory track of work in the Buildpacks public
tracker[8] that includes experimenting with hooks into the Buildpacks
staging life cycle. The intention is to provide extension points for both
application developers and operators to do things like this during staging:

* run static analysis
* run an OSS license scan
* capture the set of dependencies from the application's package manager
(pip, npm, maven, gradle, bundler, composer, etc.)
* look up the set of dependencies in the NIST vulnerability database

There's obviously a long way to go to get here, and it's not obvious how
we can implement some of this shared behavior across buildpacks and within
the buildpack app lifecycle; but we're putting a great deal of thought into
how we might make buildpacks much more flexible and extensible --
systemwide, and without having to fork them.


Thanks Mike for detailing this promising work.

Have you considered an HTTP-based API for hooking into the staging process
(as an alternative to script-based hooks mentionned into [g6]) ? This would
allow such steps to be independent of the buildpacks. Apcera pluggeable
stager model might be inspiring [g7]

One could wonder how some of the extensions you mentionned (lookup against
NIST vulnerabilty db) could be run periodically against running apps
without requiring them to restage. I guess the recent "staged droplet
download" [g8] would support such use-case.



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