Re: [Avocado-devel] [RFC] Environment Variables

[Lukáš Doktor]

Hello guys, let me just share my view (nothing radical here)

Dne 2.6.2016 v 18:13 Amador Pahim napsal(a):

On 06/01/2016 09:39 PM, Ademar Reis wrote:

On Wed, Jun 01, 2016 at 04:02:54PM -0300, Cleber Rosa wrote:

On 06/01/2016 03:07 PM, Ademar Reis wrote:

On Tue, May 31, 2016 at 07:30:43AM -0300, Cleber Rosa wrote:

I'm replying on top of Cleber because he already said a few
things I was going to say.

On 05/25/2016 05:31 AM, Amador Pahim wrote:

Hi folks,

We have requests to handle the environment variables that we can
set to
the tests. This is the RFC in that regard, with a summary of the
ideas
already exposed in the original request and some additional planning.

The original request is here:
https://trello.com/c/Ddcly0oG/312-mechanism-to-provide-environment-variables-to-tests-run-on-a-virtual-machine-remote



Motivation
==========
Avocado tests are executed in a fork process or even in a remote
machine. Regardless the fact that Avocado is hard coded to set some
environment variables, they are for internal consumption and user
is not
allowed to control/configure its behavior.

You mean this:

http://avocado-framework.readthedocs.io/en/latest/WritingTests.html#environment-variables-for-simple-tests


Right? Basically, the fact that Avocado sets some of the job/test
state as
environment variables, that can be used by SIMPLE tests.

The motivation is the request to provide users an interface to set
and/or keep environment variables for test consumption.

I'm not sure if they're necessarily for test consumption. I think
the motivation for the original request was to provide the
standard Unix interface of environment variables for when tests
are run remotely.

If the motivation is basically about setting the env vars when
running tests
remotely, than this brings the discussion about the *local* behavior to:

1. Should Avocado default to the standard UNIX behavior of cloning the
environment?

 A: IMHO, yes.

Yes

That's the current behavior (see my example at the end of the
previous email). Except when one runs tests remotely, which is
precisely the use case this feature would "fix".

Yes, agreed we should only extend the current behavior in local tests to
remote tests. That seems to be the best approach for this RFC.

2. Could Avocado have have a feature to start tests in a clean(er)
environment?

I also see a benefit, not a critical feature, though. I could imagine something like `--env-clean` which along with `--env-keep` and `--env-ignore` should cover most of the needs. It should also contain a blacklist (probably in config) to disallow overriding the reserved values.

Actually we might add the support for the `--env-ignore` even now as it could be useful (locally one can unset the variable, but remotely it's a bit harder).

 A: Possibly yes, but seems low priority.  The use case here could be
seen
as a plus in predictability, helping to achieve expected test results in
spite of the runner environment.  A real world example could be a CI
environment that sets a VERBOSE environment variable. This env var
will be
passed over to Avocado, to the test process and finally to a custom
binary
(say a benchmark tool) that will produce different output depending
on that
environment variable.  Doing that type of cleaning in the test code is
possible, but the framework could help with that.

2.1. If Avocado provides a "clean(er) test environment" feature, how to
determine which environment variables are passed along?

 A: The "env-keep" approach seems like the obvious way to do it.  If the
mechanism is enabled, which I believe should be disabled by default (see
#1), its default list could contain the more or less standard UNIX
environment variables (TERM, SHELL, LANG, etc).

Agree. But like you said such a feature would be low priority and
optional. The important thing is that the implementation of what
we're discussing in this RFC would not interfere with it.

"clean(er) test environment" would affect both local and remote
implementations and should be considered regardless this RFC. Still, I
don't see relevance in have a cleaner env right now. Agreed it's low
priority or even unwanted feature.

These environment variables can change the behavior of both
Avocado (the runner itself), the tests (after all nothing
prevents the test writer from using them) and all sub-processes
executed by the test.

Right.

Locally, this is standard:

  $ TMPDIR=/whatever/tmp VAR=foo ./avocado run test1.py

But when running avocado remotely, there's no way to configure
the environment in the destination. The environment variables set
in the command line below will not be "forwarded" to the remote
environment:

  $ TMPDIR=/whatever/tmp VAR=foo ./avocado run test1.py \
                                 --remote...

Right.

Use cases
=========
1) Use the command line or the config file to set the environment
variables in tests processes environment; access those variables from
inside the test.
2) Copy from current environment some environment variable(s) to the
tests processes environment; access those variables from inside
the test.

I think we don't even have to go that far. We can simply say the
intention is to set the environment variables in the environment
where Avocado is run. The mechanism is quite standard and well
understood.

And here comes an important point: I don't think this should be a
mechanism to pass variables to tests. Although, again,
environment variables can be used for that purpose, Avocado
should have a proper interface to provide a dictionary of
configuration and variables to each test.

The only valid reason for having such a mechanism to pass *different*
environment variables to tests, talking about local environment,
would be
*if and only if* the same environment variable to be set when running
Avocado would change the behavior of Avocado itself.  Example:

 $ AVOCADO_LOG_EARLY=1 avocado run avocado-self-tests.py

This way, both the first level avocado process (our "real" runner)
and other
instances run by the "avocado-self-test.py" code would react to that
variable. *BUT* this seems a corner case, and I wouldn't think it
justifies
the implementation of such a feature at this point.

I don't see a problem in this. When you want to debug avocado, you probably don't mind the remote avocado being also verbose. Btw this is the only way to make the remote avocado verbose as remote does not allow passing custom `--show`.

I think we should KISS: environment variables are well understood
in the Unix world. This feature will simply guarantee they (or a
subset of them) are kept when tests are run in a different
environment (remotely, in a VM, in a container -- or whatever
else we implement in the future).

Currently, this is erroneously provided by the multiplexer
(including --mux-inject), but it should be cleaned up in the near
future.

Right.

Proposal
========
- To create a command line option, under the `run` command, to set
environment variables that will be available in tests environment
process:

 $ avocado run --test-env='FOO=BAR,FOO1=BAR1' passtest.py

I can relate to this use case...

This would be a simple way of doing it, but something like
"--env-keep=FOO,FOO1" could be a better approach (more about it
below). So one would write it this way:

+1 for `--env-keep`, I'd also consider `--env-ignore` (or unset).

  $ FOO=BAR FOO1=BAR1 avocado run --env-keep='FOO,FOO1' passtest.py

Right. Again, the only drawback of --env-keep is something along the
lines
of the "AVOCADO_LOG_EARLY" example I gave earlier.

- To create an option in config file with a dictionary of environment
variables to set in test process environment. It can be used as a
replacement or complement to the command line option (with lower
priority):

 [tests.env]
 test_env_vars = {'FOO': 'BAR', 'FOO1': 'BAR1'}

... while putting those in a config file does not seem like
something one
would do.

In all cases, and more explicitly in the config file example, this
is only
really necessary if/when the environment variable to pass to the test
actually harms Avocado (considering a local execution, that is, in
a forked
process).

So, if Avocado and the test, share the use of environment variables
by the
same name, then this is a must.  Also in the case of execution in
other
"runners", such as remote/vm, this can be quite valuable.

I don't like this interface because I think this opens the door
for abuse. Like I said in a previous paragraph, this interface
should not be a mechanism for passing variables to tests.

I can also see it being abused very quickly.

- Create an option in config file with a list of environment variable
names to copy from avocado main process environment to the test
process
environment (similar to env_keep in the /etc/sudoers file):

 [tests.env]
 env_keep = ['FOO', 'FOO1', 'FOO2']

I'm not in favor of this, but I'm not strictly against it. Real world example, in our CI the `AUTOTEST_PATH` is set by default, which clashes with my custom setup, so I need to run `unset AUTOTEST_PATH` as first task in every jenkins job. I don't mind that, but a custom config with `env_unset` could solve my problem.

I like this approach because it reinforces the message that we're
keeping (or forwarding) some of the environment variables from
the original environment where the test runner was run.

Then, we need a "env_reset" mentality, and a default list of environment
variables that we forward by default (along the same lines of sudo):

Defaults    env_reset
Defaults    env_keep =  "COLORS DISPLAY HOSTNAME HISTSIZE INPUTRC KDEDIR
LS_COLORS"
Defaults    env_keep += "MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS
LC_CTYPE"
Defaults    env_keep += "LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT
LC_MESSAGES"
Defaults    env_keep += "LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER
LC_TELEPHONE"
Defaults    env_keep += "LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET
XAUTHORITY"

Like I briefly mentioned before.

That would be useful only for the use-case of resetting the
environment where *tests* are run.

As of today, there's no difference between the environment where
a test is run and the environment where the test runner is run.
They share the same variables (I like that).

The feature we're discussing would forward (keep, clone, copy,
whatever you want to call it) some of the env variables from the
env where the *original runner* is running to the env where the
*remote runner* will run. It says nothing about the env where the
actual *tests* are run. It also doesn't create any variables. It
simply forward them if they already exist in the environment.

So env_reset is not necessary. If we ever implement it, it'll
have no impact in this env-keep feature, because they'll be
working on different layers (test runner vs test).

Right, this makes sense. But it also brings the point that we may
actually
change the default behavior of keeping environment variables from
Avocado in
the tests' process.  That is, they would get a much cleaner
environment by
default.  While this sounds cleaner, it may break a lot of
expectations.

I wonder what the motivation would be to clean-up the environment
where tests are run. Can you please elaborate?  If we indeed
decide to implement this change, then I would say we should honor
whatever is set in env_keep.

I mentioned before a few points about test predictability, but the other
points that came later also support this idea.

Again, if env-keep is applicable for tests running remotely *only*, this
changes a lot of things.  If we're talking about both local and
remote, than
all what I said before applies.

There's no "local" and "remotely", because local already works.
So this feature is about extending the behavior we have locally
to remote use-cases.

For every configuration entry point, the setting have to be
respected in
local and remote executions.

Drawbacks
=========

While setting an environment variable, user will be able to change
the
behavior of a test and probably the behavior of Avocado itself. Maybe
even the OS behavior as well. We should:
- Warn users about the danger when using such options.

I fail to see where an environment variable, to be set by Avocado
in the
test process, can or should impact Avocado itself.  If it does,
then we'd
probably be doing something wrong.  I'm not sure we need warnings that
exceed documenting the intended behavior.

I think the environment has to be set where Avocado is run, not
where tests are run. Which is why I prefer --env-keep and
[env-keep].

So in the case of:

  $ FOO=bla avocado run test.py --remote=...

$FOO is available inside the environment where Avocado and its
tests are run, both locally and remotely.

Agreed, but let's just keep in mind that one (very much) corner case
(where
the environment may affect Avocado itself).

- Protect Avocado environment variables from overwriting.

About protecting the Avocado's own environment variables: agreed.

This is something that won't need any change. There are variables
which are read by Avocado and others which are written by it.

For example:

 * TMPDIR will influence Avocado's behavior (standard Unix
   variable)
 * AVOCADO_VERSION is written by Avocado. Setting it externally
   won't make any difference.

  $ TMPDIR=/home/ademar/tmp avocado run
examples/tests/env_variables.sh --show-job-log | grep Temporary
  Temporary dir: /home/ademar/tmp/avocado_L9YiE4

  $ AVOCADO_VERSION=0 ./scripts/avocado run
examples/tests/env_variables.sh --show-job-log | grep Version
  [stdout] Avocado Version: 35.0

Exactly.  Now I think I missed that fact that Avocado's own environment
variables are indeed already "protected", because they're set at when
the
SIMPLE tests' processes are created, which happens later and thus takes
precedence.

Every avocado test is a new process, so the environment setting can take place there. Then avocado is not influenced by that. So the only problem here is, that avocado overrides some values (like the AVOCADO_VERSION, or TMP), so user values will be overridden. Anyway there are not many of them so hopefully users would cope with that.

Regards,
Lukáš

Anyway, thank you, Amador, I was not happy about the `--env KEY=VALUE`, but the `--env-keep` is something I can relate to.

Yes, that's why we don't have to worry too much about the
details. The way environment variables work is quite standard and
well understood.

Agreed we should keep this simple. So right I agree we should implement
the env_keep mechanism for remote executions, using either the command
line or the config file, forwarding variables that are set locally. The
rest (set variables from command line and/or from config file, cleaner
environment,...) are not standard behavior and should not be considered
for implementation in this RFC.

I will write a V2 out of this discussion and send a PR for appreciation.

Thank you for the feedback so far.

Looking forward to read your comments.

Overall, this is definitely welcome.  Let's discuss possible
implementation
issues, such as remote/vm support, because it wouldn't be nice to
introduce
something like this with too many caveats.

We appear to have different understandings about what this
feature should be about. IMO it should be about the standard unix
environment where Avocado and tests are run. The primary use-case
is for remote/vm support (in other words, whenever there's a
change in the environment).

Then we should make it clear what we want to tackle first.  If remote/vm
support is the primary goal, then maybe we should think about
--remote-env/--vm-env options to not poison the discussion and
implementation with the env_reset/env_keep like features.

If we think env_reset is a different use-case (and based on your
use case #2 from the beginning of this e-mail looks like we do),
then indeed --remote-keep-env and --vm-keep-env are the options
we're looking for (with respective configuration file entries).

I was hoping we could implement just one "--keep-env=" instead of
multiple "--<something-remote>-keep-env=" (--remote-keep-env=,
--vm-keep-env=, --docker-keep-env=, etc), but maybe that's not a
good idea.

Thanks.
   - Ademar

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