Log and exit on metadata update errors at startup

A bad system repo can cause lorax-composer to fail to start. Instead of
a traceback log the error and exit.

(note that the exit still results in an OSError traceback due to part of
it running as root, this needs to be addressed in another commit).

src/pylorax/api/yumbase.py

@@ -24,6 +24,8 @@ from fnmatch import fnmatchcase
 from glob import glob
 import os
 import yum
+from yum.Errors import YumBaseError
+
 # This is a hack to short circuit yum's internal logging
 yum.logginglevels._added_handlers = True
 
@@ -118,6 +120,10 @@ def update_metadata(yb):
     for r in yb.repos.sort():
         r.metadata_expire = 0
         r.mdpolicy = "group:all"
-    yb.doRepoSetup()
-    yb.repos.doSetup()
-    yb.repos.populateSack(mdtype='all', cacheonly=0)
+    try:
+        yb.doRepoSetup()
+        yb.repos.doSetup()
+        yb.repos.populateSack(mdtype='all', cacheonly=0)
+    except YumBaseError as e:
+        log.error("Failed to update metadata: %s", str(e))
+        raise RuntimeError("Fetching metadata failed: %s" % str(e))

src/sbin/lorax-composer

@@ -278,7 +278,11 @@ if __name__ == '__main__':
     make_yum_dirs(server.config["COMPOSER_CFG"])
 
     # Get a YumBase to share with the requests
-    yb = get_base_object(server.config["COMPOSER_CFG"])
+    try:
+        yb = get_base_object(server.config["COMPOSER_CFG"])
+    except RuntimeError:
+        # Error has already been logged. Just exit cleanly.
+        sys.exit(1)
     server.config["YUMLOCK"] = YumLock(yb=yb, lock=Lock())
 
     # Depsolve the templates and make a note of the failures for /api/status to report