Analyze Docker Runtime Errors

Docker Runtime Error Analysis

Analyze running PHP containers for runtime failures and provide targeted diagnosis and fixes.

Runtime Error Categories

Detection Patterns

1. 502 Bad Gateway (PHP-FPM Not Running)

# FIX: Add healthcheck and proper depends_on
services:
  php-fpm:
    healthcheck:
      test: ["CMD-SHELL", "php-fpm-healthcheck || exit 1"]
      interval: 10s
      timeout: 5s
      retries: 3
  nginx:
    depends_on:
      php-fpm:
        condition: service_healthy

2. OOM Killed

; php.ini -- match memory_limit to container limit
; Container limit 256MB -> PHP memory_limit should be lower
memory_limit = 128M

# docker-compose.yml memory constraints
services:
  php-fpm:
    deploy:
      resources:
        limits:
          memory: 512M
        reservations:
          memory: 256M

3. Connection Refused

# FIX: Proper service dependencies and networking
services:
  php-fpm:
    depends_on:
      redis: { condition: service_healthy }
      database: { condition: service_healthy }
    networks: [app-network]
  redis:
    healthcheck:
      test: ["CMD", "redis-cli", "ping"]
    networks: [app-network]
  database:
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U $$POSTGRES_USER"]
    networks: [app-network]
networks:
  app-network:
    driver: bridge

4. Permission Denied (File Ownership)

# FIX: Set correct ownership in Dockerfile
RUN mkdir -p /var/www/var/cache /var/www/var/log \
    && chown -R www-data:www-data /var/www/var
COPY --chown=www-data:www-data . /var/www
USER www-data

5. PHP-FPM Pool Exhaustion

; Sizing formula: max_children = (available_memory - overhead) / avg_process_memory
; Example: (512MB - 64MB) / 32MB = ~14
[www]
pm = dynamic
pm.max_children = 14
pm.start_servers = 4
pm.min_spare_servers = 2
pm.max_spare_servers = 6
pm.max_requests = 500

6. Segmentation Fault

; Mitigation: disable problematic extensions one by one
; Common cause: OPcache + Xdebug conflict
opcache.enable=0  ; Test if OPcache causes segfault
opcache.fast_shutdown=0

Grep Patterns

# Find PHP-FPM configuration
Grep: "pm\.(max_children|start_servers|max_requests)" --glob "**/www.conf" --glob "**/php-fpm*.conf"

# Find memory_limit settings
Grep: "memory_limit" --glob "**/php.ini" --glob "**/*.ini"

# Find healthcheck definitions
Grep: "healthcheck" --glob "**/docker-compose*.yml"

# Find depends_on without condition
Grep: "depends_on:" --glob "**/docker-compose*.yml"

# Find error logging configuration
Grep: "error_log|log_errors" --glob "**/php.ini" --glob "**/*.ini"

PHP-FPM Specific Diagnostics

Severity Classification

Output Format

### Runtime Error: [Category]

**Severity:** Critical/Major/Minor
**Container:** `<service_name>`
**Log Pattern:** `<error message from logs>`

**Diagnosis:**
[Root cause analysis with evidence from logs]

**Steps to Verify:**
1. [Command to confirm the issue]
2. [Command to check related state]

**Fix:**
```yaml
# docker-compose.yml or config change

Monitoring: [How to detect this issue early in production]