Logging - Ardor Docs

Overview

Logs are your window into what’s happening inside your services. Ardor captures everything — from build output to runtime errors — so you can debug issues and monitor performance.

Cerebrum reads logs for you. Just say “why is my app crashing?” or “check the build logs” — Cerebrum will analyze logs and explain what’s wrong. The details below help you understand logs yourself.

Log Types

Ardor provides two types of logs for each service:

Build Logs

Docker build output — dependency installation, compilation, image creation

Runtime Logs

Production output — your app’s stdout/stderr while running in deployment

Build Logs

Build logs show everything that happens during docker build:

Base image download
Dependency installation (npm install, pip install, etc.)
Code compilation
Asset bundling
Any commands in your Dockerfile

What to Look For

Successful Build
Failed Build

Step 1/8 : FROM python:3.12-slim
 ---> a2c7d3e8f9b1
Step 2/8 : WORKDIR /app
 ---> Running in 3f4a5b6c7d8e
Step 3/8 : COPY requirements.txt .
 ---> 1a2b3c4d5e6f
Step 4/8 : RUN pip install --no-cache-dir -r requirements.txt
 ---> Installing collected packages: flask, click, ...
Successfully installed flask-3.0.0 ...
Step 5/8 : COPY . .
 ---> 7g8h9i0j1k2l
Step 6/8 : EXPOSE 8080
Step 7/8 : CMD ["python", "app.py"]
Successfully built 3m4n5o6p7q8r

Step 4/8 : RUN pip install --no-cache-dir -r requirements.txt
ERROR: Could not find a version that satisfies the requirement 
       nonexistent-package==1.0.0
ERROR: No matching distribution found for nonexistent-package==1.0.0
The command '/bin/sh -c pip install...' returned a non-zero code: 1

Fix: Check that all packages in requirements.txt exist and versions are correct.

Common Build Errors

Package not found

ERROR: Could not find a version that satisfies the requirement xyz

Fix: Check package name spelling, version availability, or if it’s in a private registry.

Dockerfile syntax error

failed to solve: dockerfile parse error line X: unknown instruction

Fix: Check Dockerfile syntax. Common issues: typos, missing backslashes in multi-line commands.

COPY failed: file not found

COPY failed: file not found in build context

Fix: The file doesn’t exist or isn’t committed to git. Check the path and make sure it’s not in .gitignore.

Out of memory

npm ERR! code ENOMEM

Fix: Build needs more memory. Try smaller base images or contact support for larger build instances.

Runtime Logs

Runtime logs capture your app’s output while it’s running in production:

stdout — normal output, print statements, info logs
stderr — errors, warnings, exceptions
Framework logs — web server access logs, database queries, etc.

Reading Runtime Logs

Healthy App
App with Errors

INFO:     Started server process [1]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8080
INFO:     192.168.1.1:0 - "GET /api/health HTTP/1.1" 200
INFO:     192.168.1.1:0 - "POST /api/users HTTP/1.1" 201

INFO:     Application startup complete.
ERROR:    Exception in handler:
Traceback (most recent call last):
  File "/app/routes.py", line 42, in create_user
    db.execute(query)
ConnectionRefusedError: Connection refused
ERROR:    Database connection failed - is DATABASE_URL correct?

Fix: Check your DATABASE_URL environment variable and database service status.

Adding Useful Logs

Help yourself debug by adding structured logging:

Python
Node.js

import logging

logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)

logger.info("Starting user creation", extra={"user_id": user_id})
logger.error("Failed to connect to database", exc_info=True)

const logger = {
  info: (msg, data) => console.log(JSON.stringify({ level: 'info', msg, ...data, ts: new Date() })),
  error: (msg, data) => console.error(JSON.stringify({ level: 'error', msg, ...data, ts: new Date() }))
};

logger.info('Starting user creation', { userId });
logger.error('Database connection failed', { error: err.message });

Use structured logging (JSON format) for easier searching and filtering. Include context like user IDs, request IDs, and timestamps.

How Logging Works

Zero configuration required. Ardor automatically captures everything your app writes to stdout and stderr. Just use print(), console.log(), or your favorite logging library — it all shows up in the logs.

Debugging with Logs

Startup Issues

App won’t start? Check logs in this order:

Build logs — did the image build successfully?
Runtime logs — is the app crashing on startup?
Look for: missing env vars, connection errors, port conflicts

Request Failures

API returning errors? Look for:

Stack traces with line numbers
Database query errors
External API failures
Timeout messages

Performance Issues

App slow? Look for:

Long-running queries logged with duration
Memory warnings
Connection pool exhaustion
Rate limiting messages

Log Best Practices

Log at appropriate levels

ERROR — something broke, needs attention
WARN — something unusual, might be a problem
INFO — normal operations, useful for tracking flow
DEBUG — detailed info for debugging (usually disabled in production)

Include context

Bad: "Error processing request"Good: "Error processing request user_id=123 endpoint=/api/orders error=ConnectionTimeout"

Don't log secrets

Never log passwords, API keys, or tokens. Mask sensitive data in your logging code.

Use request IDs

Generate a unique ID for each request and include it in all logs. Makes it easy to trace a request through your system.

Troubleshooting

No logs appearing

Cause: App isn’t writing to stdout/stderr, or container isn’t running.Solution:

Make sure your app logs to stdout, not to files
Check if the container is actually running (deployment status)
Verify your logging library is configured correctly

Logs cut off or missing

Cause: Very high log volume or app crashed before flushing.Solution:

Reduce log verbosity in production
Flush logs explicitly before app exit
Check for app crashes in earlier logs

Can't find specific error

Cause: Too many logs, error buried.Solution:

Use search/filter to narrow down
Filter by time when the error occurred
Search for keywords from the error message

What’s Next

Deployments

Understand the build and deploy process

Development Container

Test and debug in your dev environment

Variables & Secrets

Configure your app with environment variables

Build with Cerebrum

Let Cerebrum help you debug issues from logs

Documentation Index

​Overview

​Log Types

Build Logs

Runtime Logs

​Build Logs

​What to Look For

​Common Build Errors

​Runtime Logs

​Reading Runtime Logs

​Adding Useful Logs

​How Logging Works

​Debugging with Logs

​Startup Issues

​Request Failures

​Performance Issues

​Log Best Practices

​Troubleshooting

​What’s Next

Deployments

Development Container

Variables & Secrets

Build with Cerebrum

Overview

Log Types

Build Logs

What to Look For

Common Build Errors

Runtime Logs

Reading Runtime Logs

Adding Useful Logs

How Logging Works

Debugging with Logs

Startup Issues

Request Failures

Performance Issues

Log Best Practices

Troubleshooting

What’s Next