Update demo for tracer

experimental/example/trace_app/Dockerfile

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+FROM python:2.7
+MAINTAINER Weaveworks Inc <help@weave.works>
+WORKDIR /home/weave
+ADD requirements.txt /home/weave/
+RUN pip install -r /home/weave/requirements.txt
+ADD app.py /home/weave/
+EXPOSE 5000
+ENTRYPOINT ["python", "/home/weave/app.py"]

experimental/example/trace_app/app.py

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+import os
+import socket
+import sys
+import requests
+import random
+import threading
+import logging
+
+from concurrent.futures import ThreadPoolExecutor
+from flask import Flask
+from redis import Redis
+from werkzeug.serving import WSGIRequestHandler
+
+app = Flask(__name__)
+redis = Redis(host='redis', port=6379)
+pool = ThreadPoolExecutor(max_workers=10)
+sessions = threading.local()
+
+searchapps = ['http://searchapp:8080/']
+
+def do_redis():
+  redis.incr('hits')
+  return redis.get('hits')
+
+def do_qotd():
+  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+  try:
+    s.connect(("qotd", 4446))
+    s.send("Hello")
+    return s.recv(1024)
+  finally:
+    s.close()
+
+def do_search():
+  if getattr(sessions, 'session', None) == None:
+    sessions.session = requests.Session()
+  r = sessions.session.get(random.choice(searchapps))
+  return r.text
+
+def do_echo(text):
+  r = requests.get("http://echo/", data=text)
+  return r.text
+
+def ignore_error(f):
+  try:
+    return str(f())
+  except:
+    logging.error("Error executing function", exc_info=sys.exc_info())
+  return "Error"
+
+# this root is for the tracing demo
+@app.route('/hello')
+def hello():
+  qotd_msg = do_qotd()
+  qotd_msg = do_echo(qotd_msg)
+  return qotd_msg
+
+# this is for normal demos
+@app.route('/')
+def root():
+  #counter_future = pool.submit(do_redis)
+  #search_future = pool.submit(do_search)
+  result = do_echo(do_qotd())
+  return result
+
+if __name__ == "__main__":
+  logging.basicConfig(format='%(asctime)s %(levelname)s %(filename)s:%(lineno)d - %(message)s', level=logging.INFO)
+  WSGIRequestHandler.protocol_version = "HTTP/1.1"
+  app.run(host="0.0.0.0", port=80, debug=True)

experimental/example/trace_app/requirements.txt

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+flask
+redis
+requests
+futures