[Avocado-devel] RFC: multi-stream test (previously multi-test) [v3]
Ademar Reis
areis at redhat.com
Fri Apr 15 23:58:14 UTC 2016
On Fri, Apr 15, 2016 at 08:05:09AM +0200, Lukáš Doktor wrote:
> Hello again,
Hi Lukas.
Thanks for v3. Some inline feedback below:
>
> There were couple of changes and the new Job API RFC, which might sound
> similar to this RFC, but it covers different parts. Let's update the
> multi-test RFC and fix the terminology, which might had been a bit
> misleading.
>
> Changes:
>
> v2: Rewritten from scratch
> v2: Added examples for the demonstration to avoid confusion
> v2: Removed the mht format (which was there to demonstrate manual
> execution)
> v2: Added 2 solutions for multi-tests
> v2: Described ways to support synchronization
> v3: Renamed to multi-stream as it befits the purpose
> v3: Improved introduction
> v3: Workers are renamed to streams
> v3: Added example which uses library, instead of new test
> v3: Multi-test renamed to nested tests
> v3: Added section regarding Job API RFC
> v3: Better description of the Synchronization section
> v3: Improved conclusion
> v3: Removed the "Internal API" section (it was a transition between
> no support and "nested test API", not a "real" solution)
> v3: Using per-test granularity in nested tests (requires plugins
> refactor from Job API, but allows greater flexibility)
>
>
> The problem
> ===========
>
> Allow tests to have some if its block of code run in separate stream(s).
> We'll discuss the range of "block of code" further in the text.
>
> One example could be a user, who wants to run netperf on 2 machines, which
> requires following manual steps:
>
>
> machine1: netserver -D
> machine1: # Wait till netserver is initialized
> machine2: netperf -H $machine1 -l 60
> machine2: # Wait till it finishes and report the results
> machine1: # stop the netserver and report possible failures
>
> the test would have to contain the code for both, machine1 and machine2 and
> it executes them in two separate streams, which might or not be executed on
> the same machine.
>
> You can see that each stream is valid even without the other, so additional
> requirement would be to allow easy share of those block of codes among other
> tests. Splitting the problem in two could also sometimes help in analyzing
> the failures.
I would like to understand this requirement better, because to me
it's not clear why this is important. I think this might be a
consequence of a particular implementation, not necessarily a
requirement.
>
> Some other examples might be:
>
I suggest you add real world examples here (for a v4). My
suggestions:
> 1. A simple stress routine being executed in parallel (the same or different
> hosts)
- run a script in multiple hosts, all of them interacting with a
central service (like a DDoS test). Worth noting that this
kind of testing could also be done with the Job API.
> 2. Several code blocks being combined into a complex scenario(s)
- netperf
- QEMU live migration
- other examples?
> 3. Running the same test along with stress test in background
>
- write your own stress test and run it (inside a guest, for
example) while testing live-migration, or collecting some
performance metrics
- run bonnie or trinity in background inside the guest while
testing migration in the host
- run bonnie or trinity in background while collecting real
time metrics
> For demonstrating purposes this RFC uses a very simple example fitting in
> the category (1). It downloads the main page from "example.org" location
> using "wget" (almost) concurrently from several machines.
>
>
> Standard python libraries
> -------------------------
>
> One can run pieces of python code directly using python's multiprocessing
> library, without any need for the avocado-framework support. But there is
> quite a lot of cons:
>
> + no need for framework API
> - lots of boilerplate code in each test
> - each solution would be unique and therefor hard to analyze the logs
> - no decent way of sharing the code with other tests
>
> Yes, it's possible to share the code by writing libraries, but that does not
> scale as other solutions...
>
> Example (simplified):
>
> from avocado.core.remoter import Remote
> from threading import Thread
> ...
> class Wget(Thread):
>
> def __init__(self, machine, url):
> self.remoter = Remote(machine)
> self.url = url
> self.status = None
>
> def run(self):
> ret = self.remoter.run("wget %s" % self.target,
> ignore_status=True)
> self.status = ret.exit_status
> ...
>
> threads = []
> for machine in machines:
> threads.append(Wget(machine, "example.org"))
> for thread in threads:
> thread.start()
> for thread in threads:
> thread.join()
> self.failif(thread.status is 0, ...)
> ...
>
>
> This should serve the purpose, but to be able to understand failures, one
> would have to add a lot of additional debug information and if one wanted to
> re-use the Wget in other tests, he'd have to make it a library shared with
> all the tests.
I think we all agree this is not the way to go, so maybe you
could drop this from a potential v4 (or just be very succinct
about it).
>
> Nested tests API
> ----------------
>
> Another approach would be to say the "block of code" is the full avocado
> test. The main benefits here are, that each avocado test provides additional
> debug information in a well established format people are used to from
> normal tests, allows one to split the complex problem into separate parts
> (including separate development) and easy sharing of an existing tests (eg.
> stress test, server setup, ...) and putting them together like a Lego into
> complex scenarios.
I'm not sure we should say it's a "full avocado test". At least
for me, this sounds like a real test as run by a job, so I think
it's the wrong vocabulary.
The Test ID RFC
(https://www.redhat.com/archives/avocado-devel/2016-March/msg00024.html)
clarifies the vocabulary to use. To recapitulate and summarize:
- Test Name: A name that identifies one test (as in code to be
executed) in the context of a job. A name doesn't imply
parameters or runtime configuration.
- Test Variant: a set of runtime parameters, currently provided
by the multiplexer as AvocadoParams.
- Test Reference: whatever one provides to the test resolver
(resulting in one or more Test Names). In current Avocado, we
usually call it "test URL".
- Test: An Avocado Test instantiated and run in a Job, with its
own unique Test ID and runtime configuration. This is a
combination of a Test Name and a Test Variant that gets run in
a job.
I think we need something that would be defined as "a class that
inherits from Test". Maybe "Test Implementation", or simply "Test
Class". Then you could say that a block of code should be a "Test
Implementation" instead of using the more ambiguous and confusing
"full avocado test".
Also for this reason, I'm not a big fan of the "Nested Tests"
nomenclature. We've established long ago that we don't want
sub-tests or nested-tests inside a Job. We should make it extra
clear that a Job has no knowledge whatsoever of nested tests (and
hence I wouldn't call them "nested tests").
>
> On the negative side, avocado test is not the smallest piece of code and it
> adds quite a bit of overhead. But for simpler code, one can execute the code
> directly (threads, remoter) without a framework support.
What do you have in mind when you say "not the smallest piece of
code" and "overhead"?
>
> Example (simplified):
>
> import avocado
>
> class WgetExample(avocado.Test):
> def setUp(self):
> self.streams = avocado.Streams(self)
> for machine in machines:
> self.streams.add_stream(machine)
> def test(self)
> for stream in self.streams:
> stream.run_bg("/usr/bin/wget example.org")
> self.streams.wait(ignore_errors=False)
>
> where the `avocado.Stream` represents a worker (local or remote) which
> allows running avocado tests in it (foreground or background). This should
> provide enough flexibility to combine existing tests in complex tests.
I'm not sure I understand the purpose of the example above... You
explained you intent of using "avocado tests", but that's not
what you're doing here.
Or do you mean you're running "/usr/bin/wget example.org" as a
"simple test" (as in "not an instrumented test")?
>
> Instead of using plugin library for streams, we can develop it as another
What do you mean by "using plugin library" here?
> test variant (not a new test type, only avocado.Test with some additional
> initialization), called `avocado.MultiTest` or `avocado.NestedTest`:
>
> import avocado
>
> class WgetExample(avocado.NestedTest):
> # Machines are defined via params adn initialized
> # in NestedTest.setUp
> def test(self):
> for stream in self.streams:
> stream.run("/usr/bin/wget example.org")
> self.wait(ignore_errors=False)
I'm lost here (sorry). The only difference I see between the two
examples are:
- WgetExample now inherits from NestedTest instead of Test
- Instead of self.streams.wait(), you use self.wait().
Can you provide a more concrete example here in this section?
Maybe wget is too simplistic because it requires no
instrumentation at all. Your example from the conclusion is
better, you could have used it here.
>
>
> API backed by internal API
> ~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> _supported by cleber in v2 and I agree now_
>
> This would implement the nested test API using the internal API (from
> avocado.core).
>
> + runs native python
> + easy interaction and development
> + easily extensible by either using internal API (and risk changes) or by
> inheriting and extending the features.
> - lots of internal API will be involved, thus with almost every change of
> internal API we'd have to adjust this code to keep the NestedTest working
> - fabric/paramiko is not thread/parallel process safe and fails badly so
> first we'd have to rewrite our remote execution code (use autotest's worker,
> or aexpect+ssh)
>
>
> API backed by cmdline
> ~~~~~~~~~~~~~~~~~~~~~
>
> _liked by me in v2, hated by others, rejected in v3_
>
> This would implement the nested test API by translating it into "avocado
> run" commands.
>
> + easy to debug as users are used to the "avocado run" syntax and issues
> + allows manual mode where users trigger the "avocado run" manually
> + cmdline args are part of public API so they should stay stable
> + no issues with fabric/paramiko as each process is separate
> + even easier extensible as one just needs to implement the feature for
> "avocado run" and then can use it as extra_params in the worker, or send PR
> to support it in the stable environment.
> - would require additional features to be available on the cmdline like
> streamline way of triggering tests
> - only features available on the cmdline can be supported (currently not
> limiting)
> - rely on stdout parsing (but avocado supports machine readable output)
>
I think these two items are confusing for this RFC. We miss the
context of why they were liked or "hated". Maybe you can simply
drop them (that's how RFCs work: we refine newer versions based
on conclusions and feedback from previous discussions).
>
> Synchronization
> ===============
>
> Some tests do not need any synchronization, users just need to run them. But
> some multi-stream tests needs to be precisely synchronized or they need to
> exchange data.
>
> For synchronization purposes usually "barriers" are used, where barrier
> guards the entry into a section identified by "name" and "number of
> clients". All parties asking an entry into the section will be delayed until
> the "number of clients" reach the section (or timeout). Then they are
> resumed and can entry the section. Any failure while waiting for a barrier
> propagates to other waiting parties.
>
> This can be all automated inside the `avocado.Streams`, which could start
> listening on a free port and pass this information to the executed code
> blocks. In the code blocks one simply imports `Sync` and initialize it with
> the address+port and can use it for synchronization (or later for data
> exchange).
>
> from avocado.plugins.sync import Sync
> # Connect the sync server on address stored in params
> # which could be injected by the multi-stream test
> # or set manually.
> sync = Sync(self, params.get("sync_server", "/plugins/sync_server"))
> # wait until 2 tests ask to enter "setup" barrier (60s timeout)
> sync.barrier("setup", 2, 60)
>
> As before it can be part of the "NestedTest" test, initialized based on
> params without the need for boilerplate code. The result would be the same,
> avocado listens on some port and the tests can connect to this port and asks
> for a barrier/data exchange, with the support for re-connection.
>
> For debugging purposes it might be useful to allow starting the sync server
> as avocado plugin eg. by `--sync-server ...` (or having another command just
> to start listening, eg `avocado syncserver`). With that one could spawn the
> multiple processes manually, without the need to run the main multi-stream
> test and communicate over this manually started server, or even just debug
> the behavior of one existing piece of the bigger test and fake the other
> components by sending the messages manually instead (eg. to see how it
> handles errors, timing issues, unexpected situations).
>
> Again, there are several ways to implement this:
>
> Standard multiprocess API
> -------------------------
>
> The standard python's multiprocessing library contains over the TCP
> synchronization. The only problem is that "barriers" were introduced in
> python3 so we'd have to backport it. Additionally it does not fit 100% to
> our needs, so we'd have to adjust it a bit (eg. to allow manual interaction)
>
>
> Autotest's syncdata
> -------------------
>
> Python 2.4 friendly, supports barriers and data synchronization. On the
> contrary it's quite hackish and full of shortcuts.
>
>
> Custom code
> -----------
>
> We can inspire by the above and create simple human-readable (easy to debug
> or interact with manually) protocol to support barriers and data exchange
> via pickling. IMO that would be easier to maintain than backporting and
> adjusting of the multiprocessing or fixing the autotest syncdata. A
> proof-of-concept can be found here:
>
> https://github.com/avocado-framework/avocado/pull/1019
>
> It modifies the "passtest" to be only executed when it's executed by 2 tests
> at the same time. The proof-of-concept does not support the multi-stream
> tests, so one has to run "avocado run passtest" twice using the same
> "--sync-server" (once --sync-server and once --sync).
>
Architecturally speaking, it doesn't make much difference.
I consider this an implementation detail: the user should be free
to use whatever mechanism they want to synchronize tests. We'll
probably provide something via the avocado.utils library for
convenience.
>
> Job API RFC
> ===========
>
> Recently introduced Job API RFC covers very similar topic as "nested test",
> but it's not the same. The Job API is enabling users to modify the job
> execution, eventually even write a runner which would suit them to run
> groups of tests. On the contrary this RFC covers a way to combine
> code-blocks/tests to reuse them into a single test. In a hackish way, they
> can supplement each others, but the purpose is different.
>
> One of the most obvious differences is, that a failed "nested" test can be
> intentional (eg. reusing the NetPerf test to check if unreachable machines
> can talk to each other), while in Job API it's always a failure.
>
> I hope you see the pattern. They are similar, but on a different layer.
> Internally, though, they can share some pieces like execution the individual
> tests concurrently with different params/plugins (locally/remotely). All the
> needed plugin modifications would also be useful for both of these RFCs.
>
> Some examples:
>
> User1 wants to run "compile_kernel" test on a machine followed by
> "install_compiled_kernel passtest failtest warntest" on "machine1 machine2".
> They depend on the status of the previous test, but they don't create a
> scenario. So the user should use Job API (or execute 3 jobs manually).
>
> User2 wants to create migration test, which starts migration from machine1
> and receives the migration on machine2. It requires cooperation and together
> it creates one complex usecase so the user should use multi-stream test.
>
>
> Conclusion
> ==========
>
> Given the reasons I like the idea of "nested tests" using "API backed by
> internal API" as it is simple to start with, allows test reuse which gives
> us well known test result format and internal API allow greater flexibility
> for the future.
>
> The netperf example from introduction would look like this:
>
> Machine1:
>
> class NetServer(avocado.NestedTest):
> def setUp(self):
> process.run("netserver")
> self.barrier("setup", self.params.get("no_clients"))
> def test(self):
> pass
> def tearDown(self):
> self.barrier("finished", self.params.get("no_clients"))
> process.run("killall netserver")
>
> Machine2:
>
> class NetPerf(avocado.NestedTest):
> def setUp(self):
> self.barrier("setup", params.get("no_clients"))
> def test(self):
> process.run("netperf -H %s -l 60"
> % params.get("server_ip"))
> barrier("finished", params.get("no_clients"))
>
> One would be able to run this manually (or from build systems) using:
>
> avocado syncserver &
> avocado run NetServer --mux-inject /plugins/sync_server:sync-server
> $SYNCSERVER &
> avocado run NetPerf --mux-inject /plugins/sync_server:sync-server
> $SYNCSERVER &
>
> (where the --mux-inject passes the address of the "syncserver" into test
> params)
I think using --mux-inject should be strongly discouraged if one
is not using the multiplexer. I know that's currently the only
way to provide parameters to a test, but this should IMO be
considered a bug. Using it in a RFC may actually *encourage*
users to use it.
>
> When the code is stable one would write this multi-stream test (or multiple
> variants of them) to do the above automatically:
>
> class MultiNetperf(avocado.NestedTest):
> def setUp(self):
> self.failif(len(self.streams) < 2)
> def test(self):
> self.streams[0].run_bg("NetServer",
> {"no_clients": len(self.streams)})
> for stream in self.streams[1:]:
> stream.add_test("NetPerf",
> {"no_clients": len(self.workers),
> "server_ip": machines[0]})
> self.wait(ignore_failures=False)
I don't understand why NestedTest is used all the time. It think
it's not necessary (we could use composition instead of
inheritance).
Let me give the same example using a different API implementation
and you tell me if you see something *architecturally* wrong with
it, or if these are just *implementation details* that still
match your original idea:
netperf.py:
```
import avocado
from avocado import multi
from avocado.utils import process
class NetPerf(Test):
def test(self):
s_params = ... # server parameters
c_params = ... # client parameters
server = NetServer()
client = NetClient()
m = multi.Streams()
...
m.run_bg(server, s_params, ...)
m.run_bg(client, c_params, ...)
m.wait(ignore_errors=False)
class NetServer(multi.TestWorker)
def test(self):
process.run("netserver")
self.barrier("server", self.params.get("no_clients"))
def tearDown(self):
self.barrier("finished", self.params.get("no_clients"))
process.run("killall netserver")
class NetClient(multi.TestWorker):
def setUp(self):
self.barrier("server", params.get("no_clients"))
def test(self):
process.run("netperf -H %s -l 60"
% params.get("server_ip"))
barrier("finished", params.get("no_clients"))
`
$ avocado list netperf.py --> returns *1* Test
(NetPerf:test)
$ avocado run multi.py --> runs this *1* Test
But given multi.TestWorker is implemented as a "class that
inherit from Test", for debug purposes users could run them
individually, without any warranty or expectation that they'll
work consistently given it'll miss the instrumentation and
parameter handling that the main test does (the code from
netperf.py:NetPerf:test). Example:
$ avocado run netperf.py:NetClient
-> runs NetClient as a standalone test (in this example it
won't work unless we provide the right parameters, for
example, via the multiplexer)
$ avocado run netperf.py:NetServer
-> runs NetServer as a standalone test (same thing)
The main justification I see for the existence of test.TestWorker
is to prevent the test runner from discovering these tests by
default ('avocado run' and 'avocado list'). Maybe we could do
things differently (again, composition instead of inheritance)
and get rid of test.TestWorker. Just an idea, I'm not sure.
>
> Executing of the complex example would become:
>
> avocado run MultiNetperf
>
> You can see that the test allows running several NetPerf tests
> simultaneously, either locally, or distributed across multiple machines (or
> combinations) just by changing parameters. Additionally by adding features
> to the nested tests, one can use different NetPerf commands, or add other
> tests to be executed together.
>
> The results could look like this:
>
>
> $ tree $RESULTDIR
> └── test-results
> └── MultiNetperf
> ├── job.log
> ...
> ├── 1
> │ └── job.log
> ...
> └── 2
> └── job.log
> ...
>
> Where the MultiNetperf/job.log contains combined logs of the "master" test
> and all the "nested" tests and the sync server.
>
> Directories [12] contain results of the created (possibly even named)
> streams. I think they should be in form of standard avocado Job to keep the
> well known structure.
Only one job was executed, so there shouldn't be multiple job.log
files. The structure should be consistent with what we already
have:
$ tree job-2016-04-15T.../
job-2016-04-15T.../
├── job.log
├── id
├── replay/
├── sysinfo/
└── test-results/
├── 01-NetPerf/ (the serialized Test ID)
│ ├── data/
│ ├── debug.log
│ ├── whiteboard
│ ├── ...
│ ├── NetServer/ (a name, not a Test ID)
│ │ ├── data/
│ │ ├── ...
│ │ └── debug.log
│ └── NetClient (a name, not a Test ID)
│ ├── data/
│ ├── ...
│ └── debug.log
│
├── 02... (other Tests from the same job)
├── 03... (other Tests from the same job)
...
Finally, I suggest you also cover the other cases you introduced
in the beginning of this RFC.
For example, if multi.run() is implemented in a flexible way, we
could actually run Avocado Tests (think of Test Name) in multiple
streams:
...
from avocado import resolver
...
t = resolver("passtest.py", strict=True)
multi.run_bg(t, env1, ...)
multi.run_bg(t, env2, ...)
multi.run_bg(t, env3, ...)
multi.wait(ignore_errors=False)
Thanks.
- Ademar
--
Ademar Reis
Red Hat
^[:wq!
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