Coyote - Code Execution Service

A microservice for executing code submissions in isolated Docker containers. It listens to a Redis queue for submission requests, runs code against test cases, and stores results in PostgreSQL.

How It Works

1. Receives Submissions: Listens to a Redis pub/sub channel for code submission messages
2. Executes Code: Runs submissions in isolated Docker containers with resource limits
3. Returns Results: Stores execution results (verdict, stdout, stderr) in PostgreSQL

Supported Languages

• C (compiled with gcc, C17 standard)
• Python 3

Configuration

Configure via YAML file (see config/ directory):

env: "dev" # local, dev or prod

http:
  port: "7197" # port for accepting HTTP requests (purely for healthchecking now)

postgres:
  host: "localhost"
  port: "5432"
  user: "postgres"
  name: "postgres"
  password: "password"
  sslmode: "disable"

redis:
  addr: "localhost:6379"
  password: "password"
  db: 0

runner:
  docker_image: "ghcr.io/voidcontests/runner" # runner image, to isolate submisisons execution
  channel: "submissions" # channel where to listen for submissions

Submission Format

The service expects submission messages from Redis with the following structure:

type Submission struct {
    ID        int
    EntryID   int
    ProblemID int
    Code      string
    Language  string
}

Execution

Each submission:

• Runs in an isolated Docker container with limits:
  • 0.5 CPU cores
  • 128MB memory
  • 50 process limit
  • No network access
• Has a configurable time limit per test case
• Executes against multiple test cases stored in the database

Response

Results are stored in the database with:

• verdict: Execution verdict (AC, WA, TLE, RE, CE, etc.)
• stdout: Program output
• stderr: Error messages
• passed_tests_count: Number of test cases passed
• answer: Actual output for failed tests

Running

Native

# Build
go build -o coyote cmd/coyote/main.go

# Run with config
CONFIG_PATH=./config/dev.yaml ./coyote

Docker

# Build image
docker build -t coyote .

# Run container
docker compose up -d

Note: The service requires access to the Docker socket (/var/run/docker.sock) to run code in isolated containers.

Healthcheck

HTTP endpoint available at /api/healthcheck for service health monitoring.

curl -i localhost:7197/api/healthcheck