Add LOG_FORMAT envvar to control logging format.

docs/ENVIRONMENT.rst

@@ -64,9 +64,16 @@ Miscellaneous
 
 These environment variables are optional:
 
+* **LOG_FORMAT**
+
+  The Python logging `format string
+  <https://docs.python.org/3/library/logging.html#logrecord-attributes>`_
+  to use.  Defaults to `%(levelname)s:%(name)s:%(message)s`.
+
 * **ALLOW_ROOT**
 
-  Set this environment variable to anything non-empty to allow running ElectrumX as root.
+  Set this environment variable to anything non-empty to allow running
+  ElectrumX as root.
 
 * **NET**
 

electrumx_server.py

@@ -18,9 +18,8 @@ from server.controller import Controller
 
 def main():
     '''Set up logging and run the server.'''
-    logging.basicConfig(level=logging.INFO,
-                        format='%(asctime)s %(levelname)-7s %(message)-100s '
-                               '[%(filename)s:%(lineno)d]')
+    log_fmt = Env.default('LOG_FORMAT', '%(levelname)s:%(name)s:%(message)s')
+    logging.basicConfig(level=logging.INFO, format=log_fmt)
     logging.info('ElectrumX server starting')
     try:
         controller = Controller(Env())