Skip to main content

Common utilities for Camptocamp WSGI applications

Project description

Camptocamp WSGI utilities
=========================

This is a python 3 library providing common tools for Camptocamp WSGI
applications:

* Provide a small framework for gathering performance statistics about
a web application (statsd protocol)
* Allow to use a master/slave PostgresQL configuration
* Logging handler for CEE/UDP logs
* An optional (enabled by setting the LOG_VIEW_SECRET env var) view (/logging/level)
to change runtime the log levels
* SQL profiler to debug DB performance problems, disabled by default. You must enable it by setting the
SQL_PROFILER_SECRET env var and using the view (/sql_profiler) to switch it ON and OFF. Warning,
it will slow down everything.
* A view to get the version information about the application and the installed packages (/versions.json)
* A framework for implementing a health_check service (/health_check)
* Error handlers to send JSON messages to the client in case of error
* A cornice service drop in replacement for setting up CORS

Also provide tools for writing acceptance tests:

* A class that can be used from a py.test fixture to control a
composition
* A class that can be used from a py.text fixture to test a REST API

As an example on how to use it in an application provided by a Docker image, you can look at the
test application in [acceptance_tests/app](acceptance_tests/app).
To see how to test such an application, look at [acceptance_tests/tests](acceptance_tests/tests).


Install
-------

The library is available in PYPI:
[https://pypi.python.org/pypi/c2cwsgiutils](https://pypi.python.org/pypi/c2cwsgiutils)

With pip:
```
pip install c2cwsgiutils
```


General config
--------------

In general, configuration can be done both with environment variables (taken first) or with entries in the
`production.ini` file.

You can configure the base URL for accessing the views provided by c2cwsgiutils with an environment variable
named `C2C_BASE_PATH` or in the `production.ini` file with a property named `c2c.base_path`.


Pyramid
-------

A command line (`c2cwsgiutils_run`) is provided to start an HTTP server (gunicorn) with a WSGI application.
By default, it will load the application configured in `/app/production.ini`, but you can change that with
the `C2CWSGIUTILS_CONFIG` environment variable. All the environment variables are usable in the configuration
file using stuff like `%(ENV_NAME)s`.

To enable most of the features of c2cwsgiutils, you need to add this line to you WSGI main:

```python
import c2cwsgiutils.pyramid
config.include(c2cwsgiutils.pyramid.includeme)
```

Error catching views will be put in place to return errors as JSON.


Logging
-------

A logging backend is provided to send @cee formatted logs to syslog through UDP.
Look at the logging configuration part of
[acceptance_tests/app/production.ini](acceptance_tests/app/production.ini) for a usage example.

You can enable a view to configure the logging level on a live system using the `LOG_VIEW_SECRET` environment
variable. Then, the current status of a logger can be queried with a GET on
`{C2C_BASE_PATH}/logging/level?secret={LOG_VIEW_SECRET}&name={logger_name}` and can be changed with
`{C2C_BASE_PATH}/logging/level?secret={LOG_VIEW_SECRET}&name={logger_name}&level={level}`


Metrics
-------

To enable and configure the metrics framework, you can use:

* STATS_VIEW (c2c.stats_view): if defined, will enable the stats view `{C2C_BASE_PATH}/stats.json`
* STATSD_ADDRESS (c2c.statsd_address): if defined, send stats to the given statsd server
* STATSD_PREFIX (c2c.statsd_prefix): prefix to add to every metric names

If enabled, some metrics are automatically generated:

* {STATSD_PREFIX}.route.{verb}.{route_name}.{status}: The time to process a query (includes rendering)
* {STATSD_PREFIX}.render.{verb}.{route_name}.{status}: The time to render a query
* {STATSD_PREFIX}.sql.{query}: The time to execute the given SQL query (simplified and normalized)

You can manually measure the time spent on something like that:

```python
from c2cwsgiutils import stats
with stats.timer_context('toto', 'tutu'):
do_something()
```

Other functions exists to generate metrics. Look at the `c2cwsgiutils.stats` module.


SQL profiler
------------

The SQL profiler must be configured with the `SQL_PROFILER_SECRET` environment variable. That enables a view
to query the status of the profiler (`{C2C_BASE_PATH}/sql_profiler?secret={SQL_PROFILER_SECRET}`) or to
enable/disable it (`{C2C_BASE_PATH}/sql_profiler?secret={SQL_PROFILER_SECRET}&enable={1|0}`).

If enabled, for each `SELECT` query sent by SQLAlchemy, another query it done with `EXPLAIN ANALYZE`
prepended to it. The results are sent to the `c2cwsgiutils.sql_profiler` logger.

Don't enable that on a busy production system. It will kill your performances.


DB sessions
-----------

The `c2cwsgiutils.db.setup_session` allows you to setup a DB session that has two engines for accessing a
master/slave PostgresQL setup. The slave engine (read only) will be used automatically for `GET` and `OPTIONS`
requests and the master engine (read write) will be used for the other queries.

To use that, your production.ini must look like that:

```ini
sqlalchemy.url = %(SQLALCHEMY_URL)s
sqlalchemy.pool_recycle = 30
sqlalchemy.pool_size = 5
sqlalchemy.max_overflow = 25

sqlalchemy_slave.url = %(SQLALCHEMY_URL_SLAVE)s
sqlalchemy_slave.pool_recycle = 30
sqlalchemy_slave.pool_size = 5
sqlalchemy_slave.max_overflow = 25
```

And your code that initializes the DB connection must look like that:

```python
from c2cwsgiutils.db import setup_session
def init(config):
global DBSession
DBSession = setup_session(config, 'sqlalchemy', 'sqlalchemy_slave', force_slave=[
"POST /api/hello"
])[0]
```

You can use the `force_slave` and `force_master` parameters to override the defaults and force a route to use
the master or the slave engine.


Health checks
-------------

To enable health checks, you must add some setup in your WSGI main (usually after the DB connections are
setup). For example:

```python
from c2cwsgiutils.health_check import HealthCheck

def custom_check(request):
global not_happy
if not_happy:
raise Exception("I'm not happy")

health_check = HealthCheck(config)
health_check.add_db_session_check(models.DBSession, at_least_one_model=models.Hello)
health_check.add_url_check('http://localhost/api/hello')
health_check.add_custom_check('custom', custom_check, 2)
```

Then, the URL `{C2C_BASE_PATH}/health_check?max_level=2` can be used to run the health checks and get a report
looking like that (in case of error):

```json
{
"status": 500,
"successes": ["db_engine_sqlalchemy", "db_engine_sqlalchemy_slave", "http://localhost/api/hello"],
"failures": {
"custom": {
"message": "I'm not happy"
}
}
}
```


SQLAlchemy models graph
-----------------------

A command is provided that can generate Doxygen graphs of an SQLAlchemy ORM model.
See [acceptance_tests/app/models_graph.py](acceptance_tests/app/models_graph.py) how it's used.


Version information
-------------------

If the `/app/versions.json` exists, a view is added (`{C2C_BASE_PATH}/version.json`) to query the current
version of a app. This file is generated by calling the `c2cwsgiutils_genversion.py $GIT_TAG $GIT_HASH`
command line. Usually done in the [Dockerfile](acceptance_tests/app/Dockerfile) of the WSGI application.


Debugging
---------

To enable the debugging interface, you must set the `DEBUG_VIEW_SECRET` environment variable or the
`c2c.debug_view_secret` variable. Then you can get a dump of every threads with this URL:
`{C2C_BASE_PATH}/debug/stacks?secret={DEBUG_VIEW_SECRET}`


CORS
----

To have CORS compliant views, define your views like that:

```python
from c2cwsgiutils import services
hello_service = services.create("hello", "/hello", cors_credentials=True)

@hello_service.get()
def hello_get(request):
return {'hello': True}
```


Developer info
==============

You will need `docker` (>=1.12.0), `docker-compose` (>=1.10.0), twine and
`make` installed on the machine to play with this project.
Check available versions of `docker-engine` with
`apt-get policy docker-engine` and eventually force install the
up-to-date version using a command similar to
`apt-get install docker-engine=1.12.3-0~xenial`.

To lint and test everything, run the following command:

```shell
make
```

Make sure you are strict with the version numbers:

* bug fix version change: Nothing added, removed or changed in the API and only bug fix
version number changes in the dependencies
* minor version change: The API must remain backward compatible and only minor version
number changes in the dependencies
* major version change: The API and the dependencies are not backward compatible

To make a release:

* Change the the version in [setup.py](setup.py)
* run `make release`


Project details


Release history Release notifications | RSS feed

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distributions

No source distribution files available for this release.See tutorial on generating distribution archives.

Built Distribution

c2cwsgiutils-0.11.1-py3-none-any.whl (29.7 kB view hashes)

Uploaded Python 3

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page