Allow logging as json

This will help for the part of the infrastructure not using systemd/journald
log to push introspectable logs.

Ref. swh/infra/sysadm-environment#4524

mypy.ini

@@ -43,3 +43,6 @@ ignore_missing_imports = True
 
 [mypy-simpy.*]
 ignore_missing_imports = True
+
+[mypy-pythonjsonlogger.*]
+ignore_missing_imports = True

requirement-logger-json.txt

+python-json-logger

setup.py

@@ -53,6 +53,7 @@ setup(
         "testing": parse_requirements("test", "journal", "simulator"),
         "journal": parse_requirements("journal"),
         "simulator": parse_requirements("simulator"),
+        "logger-json": parse_requirements("logger-json"),
     },
     include_package_data=True,
     entry_points="""

swh/scheduler/celery_backend/config.py

@@ -94,6 +94,8 @@ def setup_log_handler(
         log_console = True
     elif log_target == "journal":
         log_journal = True
+    elif log_target == "json":
+        log_json = True
 
     # this looks for log levels *higher* than DEBUG
     if loglevel <= logging.DEBUG and log_console is None:
@@ -118,6 +120,14 @@ def setup_log_handler(
             systemd_journal.setFormatter(formatter)
             root_logger.addHandler(systemd_journal)
 
+    if log_json:
+        from pythonjsonlogger import jsonlogger
+
+        json_handler = logging.StreamHandler()
+        formatter = jsonlogger.JsonFormatter()
+        json_handler.setFormatter(formatter)
+        root_logger.addHandler(json_handler)
+
     logging.getLogger("celery").setLevel(logging.INFO)
 
     # Silence amqp heartbeat_tick messages

tox.ini

@@ -38,6 +38,7 @@ commands =
 [testenv:mypy]
 extras =
   testing
+  logger-json
 deps =
   mypy==0.942
 commands =
@@ -51,6 +52,7 @@ whitelist_externals = make
 usedevelop = true
 extras =
   testing
+  logger-json
 deps =
   # fetch and install swh-docs in develop mode
   -e git+https://forge.softwareheritage.org/source/swh-docs#egg=swh.docs
@@ -70,6 +72,7 @@ whitelist_externals = make
 usedevelop = true
 extras =
   testing
+  logger-json
 deps =
   # install swh-docs in develop mode
   -e ../swh-docs