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Merged
tonyandrewmeyer merged 3 commits into from
Jul 4, 2025
Merged

docs: use load_config in the httpbin example charm #1852

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c15a677
docs: use load_config in the httpbin example charm.
tonyandrewmeyer Jun 26, 2025
de295f1
Update examples/httpbin-demo/requirements.txt
tonyandrewmeyer Jul 1, 2025
7fe4e59
Add comment, per review.
tonyandrewmeyer Jul 1, 2025
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2 changes: 1 addition & 1 deletion examples/httpbin-demo/requirements.txt
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Original file line number Diff line number Diff line change
@@ -1 +1 @@
ops>2,<4
ops>=2.23,<4 # Version 2.23 introduced the load_config() method.
48 changes: 37 additions & 11 deletions examples/httpbin-demo/src/charm.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@

"""Charm the service."""

import dataclasses
import logging
import time

Expand All @@ -24,11 +25,31 @@
# Log messages can be retrieved using juju debug-log.
logger = logging.getLogger(__name__)

VALID_LOG_LEVELS = ['info', 'debug', 'warning', 'error', 'critical']
CONTAINER_NAME = 'httpbin' # Name of workload container.
SERVICE_NAME = 'httpbin' # Name of Pebble service that runs in the workload container.


@dataclasses.dataclass(frozen=True)
class HttpbinConfig:
"""Schema for the configuration of the httpbin charm."""

log_level: str = 'info'
"""Configures the log level of gunicorn.

Acceptable values are: "info", "debug", "warning", "error" and "critical".
"""

def __post_init__(self):
log_level = self.log_level.lower()
valid_log_levels = {'info', 'debug', 'warning', 'error', 'critical'}
if log_level not in valid_log_levels:
raise ValueError(
f"Invalid log level: '{self.log_level}'. "
f'Valid values are: {", ".join(valid_log_levels)}.'
)
object.__setattr__(self, 'log_level', log_level)


class HttpbinDemoCharm(ops.CharmBase):
"""Charm the service."""

Expand All @@ -41,9 +62,10 @@ def __init__(self, framework: ops.Framework):

def _on_collect_status(self, event: ops.CollectStatusEvent):
"""Report the status of the workload (runs after each event)."""
log_level = str(self.config['log-level']).lower()
if log_level not in VALID_LOG_LEVELS:
event.add_status(ops.BlockedStatus(f"invalid log level: '{log_level}'"))
try:
self.load_config(HttpbinConfig)
except ValueError as e:
event.add_status(ops.BlockedStatus(str(e)))
try:
if not self.container.get_service(SERVICE_NAME).is_running():
# We can connect to Pebble in the container, but the service hasn't started yet.
Expand All @@ -64,11 +86,14 @@ def _on_collect_status(self, event: ops.CollectStatusEvent):

def _on_httpbin_pebble_ready(self, event: ops.PebbleReadyEvent):
"""Define and start a workload using the Pebble API."""
log_level = str(self.config['log-level']).lower()
if log_level not in VALID_LOG_LEVELS:
try:
config = self.load_config(HttpbinConfig)
except ValueError:
return
# Add initial Pebble config layer using the Pebble API.
self.container.add_layer('httpbin', self._make_pebble_layer(log_level), combine=True)
self.container.add_layer(
'httpbin', self._make_pebble_layer(config.log_level), combine=True
)
# Make Pebble reevaluate its plan, ensuring any services are started if enabled.
self.container.replan()
# In rare cases, these calls could fail because the workload container became unavailable.
Expand All @@ -77,16 +102,17 @@ def _on_httpbin_pebble_ready(self, event: ops.PebbleReadyEvent):

def _on_config_changed(self, event: ops.ConfigChangedEvent):
"""Handle changed configuration."""
log_level = str(self.config['log-level']).lower()
if log_level not in VALID_LOG_LEVELS:
try:
config = self.load_config(HttpbinConfig)
except ValueError:
return
# Update the configuration of the workload.
# We might not be able to access the workload container yet, so we'll try a few times.
max_attempts = 3
for attempt in range(max_attempts):
try:
self.container.add_layer(
'httpbin', self._make_pebble_layer(log_level), combine=True
'httpbin', self._make_pebble_layer(config.log_level), combine=True
)
self.container.replan()
except (ops.pebble.APIError, ops.pebble.ConnectionError): # noqa: PERF203 (try-except in loop)
Expand All @@ -99,7 +125,7 @@ def _on_config_changed(self, event: ops.ConfigChangedEvent):
# We expect that there'll be a pebble-ready event in the future,
# which will configure and start the workload.
return
logger.debug("Log level for gunicorn changed to '%s'", log_level)
logger.debug("Log level for gunicorn changed to '%s'", config.log_level)

def _make_pebble_layer(self, log_level: str) -> ops.pebble.LayerDict:
"""Return a dictionary representing a Pebble layer."""
Expand Down