Add a discovery implementation in Python.

.drone.yml

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+image: python2.7
+notify:
+  email:
+    recipients:
+    - drone@clever.com
+script:
+  - make test

CHANGES.md

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+## 0.1.0 (2016-03-11)
+- Initial version.

Makefile

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+.PHONY: all clean deps format lint publish test
+SHELL := /bin/bash
+
+all: format lint test
+
+clean:
+	find -type f -name '*.pyc' -delete
+
+deps:
+	python setup.py develop
+
+format:
+	autopep8 -i -r -j0 -a --experimental --max-line-length 100 --indent-size 2 .
+
+lint:
+	pep8 --config ./pep8 . || true
+
+publish:
+	./publish.sh
+
+test: deps
+	nosetests ./test

README.md

@@ -1,2 +1,84 @@
 # discovery-python
-Programmatically find service endpoints (i.e. discovery-go for python)
+
+Programmatically find service endpoints.
+
+This library currently is just an abstraction around reading environment variables used for dependent services.
+
+## Installation
+
+### pip
+
+```sh
+pip install git+https://<clever-drone Github token>@github.com/Clever/discovery-python.git@<version_tag>
+```
+
+The Github token can be found in [dev-passwords](https://github.com/Clever/clever-ops/tree/master/credentials).
+
+### setup.py
+
+```python
+from setuptools import setup
+
+# Assuming discovery v0.1.0 is being installed:
+setup(
+
+    # ...
+
+    install_requires=['discovery==0.1.0'],
+    dependency_links=[
+      'https://<clever-drone Github token>@github.com/Clever/discovery-python/tarball/v0.1.0#egg=discovery-0.1.0'
+    ],
+
+    # ...
+
+)
+```
+
+The Github token can be found in [dev-passwords](https://github.com/Clever/clever-ops/tree/master/credentials).
+
+## Usage
+
+```python
+import discovery
+
+try:
+	redis_url = discovery.url('redis', 'tcp')
+
+	redis_host_and_port = discovery.host_port('redis', 'tcp')
+
+	redis_host = discovery.host('redis', 'tcp')
+
+	redis_port = discovery.port('redis', 'tcp')
+
+except discovery.MissingEnvironmentVariableError as e:
+	print 'ERROR: Redis discovery failed: {}.'.format(e)
+
+```
+
+## Environment Variables
+
+This library currently requires environment variables to be defined in the following format:
+
+```
+SERVICE_{SERVICE_NAME}_{EXPOSE}_{PROTO|HOST|PORT}
+```
+
+### Example:
+```bash
+SERVICE_REDIS_TCP_PROTO = "tcp"
+SERVICE_REDIS_TCP_HOST = "localhost"
+SERVICE_REDIS_TCP_PORT = "6379"
+```
+
+## Development
+
+### Publishing a new version
+
+1. Bump the version in the `VERSION` file and update the changelog in `CHANGES.md`.
+2. Merge your changes into `master`.
+3. Checkout `master`
+4. Run the publish script:
+
+    ```sh
+    ./publish.sh
+    ```

VERSION

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+0.1.0

discovery/__init__.py

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+from __future__ import absolute_import
+
+from .discovery import *

discovery/discovery.py

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+import logger
+import os
+
+
+_ENV_VAR_TEMPLATE = 'SERVICE_{service_name}_{expose}_{component}'
+
+
+def url(service_name, expose):
+  """
+  Returns the URL for the given service and exposed interface, based on
+  environment variables of the form
+  `SERVICE_{SERVICE NAME}_{EXPOSE}_{PROTO|HOST|PORT}`.
+  """
+  return '{}://{}'.format(proto(service_name, expose), host_port(service_name, expose))
+
+
+def host_port(service_name, expose):
+  """
+  Returns a `{HOST}:{PORT}` string for the given service and exposed interface,
+  based on environment variables of the form
+  `SERVICE_{SERVICE NAME}_{EXPOSE}_{HOST|PORT}`.
+  """
+  return '{}:{}'.format(host(service_name, expose), port(service_name, expose))
+
+
+def host(service_name, expose):
+  """
+  Returns the host name for the given service and exposed interface, based on
+  environment variables of the form `SERVICE_{SERVICE NAME}_{EXPOSE}_{HOST}`.
+  """
+  return _get_env_var(service_name, expose, 'HOST')
+
+
+def port(service_name, expose):
+  """
+  Returns the port for the given service and exposed interface, based on
+  environment variables of the form `SERVICE_{SERVICE NAME}_{EXPOSE}_{PROTO}`.
+  """
+  return _get_env_var(service_name, expose, 'PORT')
+
+
+def proto(service_name, expose):
+  """
+  Returns the protocol for the given service and exposed interface, based on
+  environment variables of the form `SERVICE_{SERVICE NAME}_{EXPOSE}_{PROTO}`.
+  """
+  return _get_env_var(service_name, expose, 'PROTO')
+
+
+def _get_env_var(service_name, expose, component):
+  var_name = _ENV_VAR_TEMPLATE.format(
+      service_name=service_name, expose=expose, component=component)
+  var_name = var_name.upper().replace('-', '_')
+
+  value = os.environ.get(var_name)
+  if (value is None):
+    raise MissingEnvironmentVariableError(var_name)
+
+  return value
+
+
+class MissingEnvironmentVariableError(Exception):
+
+  """Raised when a required environment cannot be found."""
+
+  def __init__(self, var_name):
+    self.var_name = var_name
+
+  def __str__(self):
+    return 'Missing environment variable `{}`.'.format(self.var_name)

pep8

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+[pep8]
+ignore = E111
+exclude = ./.eggs
+max-line-length = 100

publish.sh

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+#!/bin/bash
+
+# Creates git tags!
+# Reads version from VERSION file.
+
+version=`cat VERSION`
+changelog=CHANGES.md
+grep $version $changelog >> /dev/null
+if [[ $? -ne 0 ]]; then
+  echo "Couldn't find version $version in $changelog"
+  exit
+fi
+
+read -p "Tag as v$version? [y/n] " -n 1 -r
+if [[ $REPLY =~ ^[Yy]$ ]]; then
+  # create git tags
+  git tag -a v$version -m "version $version"
+  git push --tags
+fi

requirements-dev.txt

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+-r requirements.txt
+nose>=1.0

requirements.txt

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+kayvee==2.0.1

setup.py

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+#!/usr/bin/env python
+
+import os
+import sys
+from setuptools import setup, find_packages
+from pip.req import parse_requirements
+
+import pkg_resources
+
+here = os.path.abspath(os.path.dirname(__file__))
+
+with open(os.path.join(here, 'VERSION')) as f:
+  VERSION = f.read().strip()
+
+pr_kwargs = {}
+if pkg_resources.get_distribution("pip").version >= '6.0':
+  pr_kwargs = {"session": False}
+
+install_reqs = parse_requirements(
+    os.path.join(
+        here,
+        './requirements.txt' if not sys.argv[1] in ['develop', 'test'] else './requirements-dev.txt'
+    ), **pr_kwargs)
+
+setup(
+    name='discovery',
+    version=VERSION,
+    author='Clever (https://clever.com)',
+    author_email='tech-notify@clever.com',
+    url='https://github.com/Clever/discovery-python/',
+    packages=['discovery'],
+    install_requires=[str(ir.req) for ir in install_reqs],
+    setup_requires=['nose>=1.0'],
+    test_suite='nose.collector',
+    long_description="""\
+    Programmatically find service endpoints.
+    """
+)

test/test_discovery.py

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+import discovery
+import os
+import unittest
+
+from discovery import MissingEnvironmentVariableError
+
+
+class TestDiscovery(unittest.TestCase):
+
+  def test_host_available(self):
+    host = 'host-available.ops.clever.com'
+    os.environ['SERVICE_HOST_AVAILABLE_TCP_HOST'] = host
+
+    self.assertEqual(discovery.host('host-available', 'tcp'), host)
+
+  def test_host_missing(self):
+    with self.assertRaisesRegexp(MissingEnvironmentVariableError, 'SERVICE_HOST_MISSING_HTTP_HOST'):
+      discovery.host('host-missing', 'http')
+
+  def test_port_available(self):
+    port = '5000'
+    os.environ['SERVICE_PORT_AVAILABLE_TCP_PORT'] = port
+
+    self.assertEqual(discovery.port('port-available', 'tcp'), port)
+
+  def test_port_missing(self):
+    with self.assertRaisesRegexp(MissingEnvironmentVariableError, 'SERVICE_PORT_MISSING_HTTP_PORT'):
+      discovery.port('port-missing', 'http')
+
+  def test_proto_available(self):
+    proto = 'http'
+    os.environ['SERVICE_PROTO_AVAILABLE_TCP_PROTO'] = proto
+
+    self.assertEqual(discovery.proto('proto-available', 'tcp'), proto)
+
+  def test_proto_missing(self):
+    with self.assertRaisesRegexp(
+            MissingEnvironmentVariableError, 'SERVICE_PROTO_MISSING_HTTP_PROTO'):
+      discovery.proto('proto-missing', 'http')
+
+  def test_host_port_available(self):
+    host = 'host-port-available.ops.clever.com'
+    os.environ['SERVICE_HOST_PORT_AVAILABLE_HTTP_HOST'] = host
+
+    port = '5000'
+    os.environ['SERVICE_HOST_PORT_AVAILABLE_HTTP_PORT'] = port
+
+    self.assertEqual(discovery.host_port('host-port-available', 'http'), '{}:{}'.format(host, port))
+
+  def test_host_port_missing_port(self):
+    host = 'port-missing.ops.clever.com'
+    os.environ['SERVICE_PORT_MISSING_HTTP_HOST'] = host
+
+    with self.assertRaisesRegexp(MissingEnvironmentVariableError, 'SERVICE_PORT_MISSING_HTTP_PORT'):
+      discovery.host_port('port-missing', 'http')
+
+  def test_url_available(self):
+    proto = 'http'
+    os.environ['SERVICE_URL_AVAILABLE_BLAH_PROTO'] = proto
+
+    host = 'user:pasws@url-available.ops.clever.com'
+    os.environ['SERVICE_URL_AVAILABLE_BLAH_HOST'] = host
+
+    port = '9090'
+    os.environ['SERVICE_URL_AVAILABLE_BLAH_PORT'] = port
+
+    self.assertEqual(discovery.url('url-available', 'blah'), '{}://{}:{}'.format(proto, host, port))
+
+  def test_url_missing_host(self):
+    proto = 'tcp'
+    os.environ['SERVICE_PROTO_MISSING_TCP_PROTO'] = proto
+
+    port = '9090'
+    os.environ['SERVICE_PROTO_MISSING_TCP_PORT'] = port
+
+    with self.assertRaisesRegexp(MissingEnvironmentVariableError, 'SERVICE_PROTO_MISSING_TCP_HOST'):
+      discovery.url('proto-missing', 'tcp')