Outputting to Log Files

Problem Definition

Console output flows by and cannot be referenced later. You want to save logs to files and search with familiar tools like grep.

How to do it

Specify the log output destination file with the --log-file option.

# Output logs to file
./actor_iac.java run -w sysinfo/main-collect-sysinfo.yaml -i inventory.ini --log-file ./logs/sysinfo.log

# Suppress console output and output only to file
./actor_iac.java run -w sysinfo/main-collect-sysinfo.yaml -i inventory.ini --log-file ./logs/sysinfo.log --quiet

Log files are saved in the same format as console output.

$ cat ./logs/sysinfo.log
[cli] 2026-01-15 10:00:00 INFO Loading workflow: main-collect-sysinfo.yaml
[cli] 2026-01-15 10:00:00 INFO Created 6 node actors for group 'compute'
[node-node13] ===== HOSTNAME =====
[node-node13] node13.local
...

You can extract specific node output with grep.

# Extract only node13 logs
grep "^\[node-node13\]" ./logs/sysinfo.log

# Extract only errors
grep "ERROR" ./logs/sysinfo.log

# Extract GPU information
grep -A1 "GPU INFO" ./logs/sysinfo.log

Under the hood

Why file output is fast:

Destination	Mechanism	Speed
System.out	Synchronous, no buffering	Slow
File	BufferedWriter, OS buffering	Fast

System.out outputs synchronously for each line, so blocking occurs with large output. File output uses BufferedWriter and is also buffered at the OS level, minimizing I/O waiting.

Choosing between log files and log database:

Method	Advantages	Disadvantages
Log file	Simple, searchable with grep	Difficult to integrate searches across multiple executions
Log database	Flexible search with SQL, session management	Setup required

Log files are suitable for checking results of single executions, while log databases are suitable for accumulating logs in continuous operation.

Derived Problems and Solutions

Problem: Directory fills up with log files

If log file output is enabled by default, log files are generated every time you work with actor-IaC, and the directory fills up with log files.

Solution: Default is OFF, specify only when needed

The --log-file option is OFF by default. Explicitly specify it only for executions where you want to save logs.

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Problem: Log file becomes bloated

If you keep specifying the same filename, the log file becomes too large.

Solution: Use timestamped filenames

Specify different filenames for each execution.

# Include datetime in filename
./actor_iac.java run -w sysinfo/main-collect-sysinfo.yaml -i inventory.ini \
  --log-file "./logs/sysinfo-$(date +%Y%m%d-%H%M%S).log"

Alternatively, use log rotation tools (logrotate, etc.).