joblet

Process Isolation in Joblet

Joblet provides complete process isolation using Linux PID namespaces, ensuring that jobs run in their own isolated process environment with complete separation from the host system.

How Process Isolation Works

When you run a job with rnx job run, Joblet:

1. Creates a PID namespace - The job gets its own process space
2. Makes job process PID 1 - Your command becomes the init process in the namespace
3. Isolates process visibility - Jobs can only see their own process tree
4. Preserves parent-child relationships - Child processes are visible with proper PIDs

Process Hierarchy

In the isolated namespace:

• PID 1: Your main job command (acts as init)
• PID 2+: Any child processes spawned by your job
• No system processes: Host system processes are completely hidden

Examples

Example 1: Simple Process with Children

Create a job that spawns multiple child processes:

rnx job run --runtime=python-3.11-ml bash -c "sleep 30 & sleep 40 & ps aux"

Output:

USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
0              1  1.0  0.1   4364  2916 ?        S    05:40   0:00 /usr/bin/bash -c sleep 30 & sleep 40 & ps aux
0              7  0.0  0.0   2792   280 ?        S    05:40   0:00 sleep 30
0              8  0.0  0.0   2792   280 ?        S    05:40   0:00 sleep 40
0              9  0.0  0.1   7064  2300 ?        R    05:40   0:00 ps aux

Process Tree:

• PID 1: Main bash process (parent)
• PID 7: First sleep process (child)
• PID 8: Second sleep process (child)
• PID 9: ps command (child)

Example 2: Complex Multi-Process Job

Create a more complex job with different types of processes:

rnx job run --runtime=python-3.11-ml bash -c "echo 'Starting processes...' && sleep 60 & echo 'Sleep started' && python3 -c 'import time; [print(f\"Python process {i}\") or time.sleep(1) for i in range(5)]' & echo 'Python started' && ps aux && echo 'Waiting for processes...' && wait"

Process Tree Shows:

• PID 1: Main bash process (parent)
• PID 6-7: Subshell processes
• PID 8: sleep 60 (background child)
• PID 9: python3 process (background child)
• PID 10: ps aux command (foreground child)

Example 3: Process Synchronization

Create processes and wait for them to complete:

rnx job run --runtime=python-3.11-ml bash -c "(sleep 10; echo 'Child 1 done') & (sleep 15; echo 'Child 2 done') & echo 'Both children started' && ps aux && wait && echo 'All processes completed'"

This demonstrates:

• Background processes with subshells
• Process synchronization using wait
• Complete process lifecycle visibility

Key Benefits

1. Authentic Isolated Experience

• Job process naturally becomes PID 1
• Child processes get sequential PIDs (2, 3, 4, etc.)
• No fake process renumbering or filtering

2. Complete Process Tree Visibility

• See all processes spawned by your job
• Parent-child relationships are preserved
• Real-time process monitoring with ps, top, etc.

3. Perfect Isolation

• No host system processes visible
• Cannot see other jobs’ processes
• Complete process namespace separation

4. Standard Process Management

• Use standard tools: ps, kill, jobs, wait
• Signal handling works normally
• Process groups and sessions work as expected

Process Management Commands

All standard Linux process management commands work within the isolated namespace:

# View all processes in your job
rnx job run --runtime=python-3.11-ml ps aux

# Monitor processes in real-time
rnx job run --runtime=python-3.11-ml top

# Create background processes
rnx job run --runtime=python-3.11-ml bash -c "long-running-task &"

# Wait for background processes
rnx job run --runtime=python-3.11-ml bash -c "background-task & wait"

# Kill specific processes (by PID within namespace)
rnx job run --runtime=python-3.11-ml bash -c "sleep 60 & kill %1"

Technical Implementation

Joblet achieves process isolation through:

1. Linux PID Namespaces: Creates isolated process space
2. Process Replacement: Uses exec to replace init with job command
3. Filesystem Isolation: Remounts /proc to show only namespace processes
4. cgroup Integration: Resource limits apply to entire process tree

Comparison with Container Solutions

Feature	Joblet	Traditional Containers
Process becomes PID 1	✅	✅
Child process visibility	✅	✅
Host process isolation	✅	✅
Standard process tools	✅	✅
Resource limits	✅	✅
Network isolation	✅	✅
Lightweight execution	✅	❌
No image management	✅	❌

Best Practices

1. Process Cleanup

Always ensure child processes are cleaned up:

# Good: Wait for all background processes
rnx job run --runtime=python-3.11-ml bash -c "task1 & task2 & wait"

# Good: Trap signals for cleanup
rnx job run --runtime=python-3.11-ml bash -c "trap 'kill $(jobs -p)' EXIT; task1 & task2 & wait"

2. Resource Management

Monitor process resource usage:

# Monitor memory and CPU usage
rnx job run --runtime=python-3.11-ml bash -c "memory-intensive-task & top -p \$!"

3. Error Handling

Handle process failures gracefully:

# Check background process status
rnx job run --runtime=python-3.11-ml bash -c "risky-task & wait \$! || echo 'Task failed'"

Security Implications

Process isolation provides strong security boundaries:

• No process interference: Jobs cannot affect other jobs’ processes
• No host visibility: Cannot see or interact with host system processes
• Resource isolation: Process limits are enforced at the cgroup level
• Signal isolation: Cannot send signals to processes outside the namespace

This ensures complete process-level security between jobs and from the host system.

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