Feature 10961 Addition of external targets to OSM Prometheus

This commit allows the automatic regeneration of a Prometheus config
file from a sidecar by combining the information in PROMETHEUS_BASE_CONFIG_FILE
and the prometheus_jobs in mongo.

Change-Id: I0246d60ec32733a088ca8590a6445735549bf4de
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/docker/Prometheus/src/app.py b/docker/Prometheus/src/app.py
index 43cca08..157413d 100755
--- a/docker/Prometheus/src/app.py
+++ b/docker/Prometheus/src/app.py
@@ -37,6 +37,7 @@
 mongodb_url = os.environ["MONGODB_URL"]
 target_database = os.environ["TARGET_DATABASE"]
 prometheus_config_file = os.environ["PROMETHEUS_CONFIG_FILE"]
+prometheus_base_config_file = os.environ["PROMETHEUS_BASE_CONFIG_FILE"]
 prometheus_url = os.environ["PROMETHEUS_URL"]
 
 
@@ -63,19 +64,12 @@
 
 
 def generate_prometheus_config(prometheus_jobs, config_file_path):
-    config_file = open(config_file_path, encoding="utf-8", mode="r")
-    config_file_contents = config_file.read()
-    config_file.close()
-
-    config_file_yaml = yaml.load(config_file_contents, yaml.FullLoader)
+    with open(config_file_path, encoding="utf-8", mode="r") as config_file:
+        config_file_yaml = yaml.safe_load(config_file)
     if config_file_yaml is None:
         config_file_yaml = {}
-
-    if len(prometheus_jobs) == 0:
+    if "scrape_configs" not in config_file_yaml:
         config_file_yaml["scrape_configs"] = []
-        return config_file_yaml
-
-    config_file_yaml["scrape_configs"] = []
 
     for prometheus_job in prometheus_jobs:
         cleaned_up_job = clean_up_job(prometheus_job)
@@ -129,12 +123,12 @@
     stored_jobs = get_jobs(client)
     print(f"Jobs detected : {len(stored_jobs):d}")
     generated_prometheus_config = generate_prometheus_config(
-        stored_jobs, prometheus_config_file
+        stored_jobs, prometheus_base_config_file
     )
     print(f"Writing new config file to {prometheus_config_file}")
     config_file = open(prometheus_config_file, "w")
     config_file.truncate(0)
-    config_file.write(yaml.dump(generated_prometheus_config))
+    config_file.write(yaml.safe_dump(generated_prometheus_config))
     config_file.close()
     print("New config written, updating prometheus")
     update_resp = await reload_prometheus_config(prometheus_url)