# PR: feat: Add dockerArgs field to catalog schema
## Repository
`docker/mcp-gateway`
## Title
feat(catalog): Add dockerArgs field for custom Docker run arguments
## Description
This PR adds a `dockerArgs` field to the catalog schema, allowing MCP server authors to specify custom Docker run arguments.
### Motivation
Many advanced MCP servers require Docker options that aren't currently exposed:
| Use Case | Required Args |
|----------|---------------|
| Chrome DevTools (localhost access) | `--network host` |
| Local LLM inference | `--gpus all` |
| Audio processing | `--device /dev/snd` |
| Privileged operations | `--cap-add SYS_PTRACE` |
| Custom DNS | `--dns 8.8.8.8` |
Without this field, the Gateway is limited to "vanilla" containers, blocking many legitimate use cases.
### Proposed Schema Change
```yaml
# Before (current)
my-server:
image: my-image:latest
env:
- name: FOO
value: bar
# After (with dockerArgs)
my-server:
image: my-image:latest
dockerArgs:
- "--network"
- "host"
- "--gpus"
- "all"
env:
- name: FOO
value: bar
```
### Implementation
In the gateway code that builds the `docker run` command:
```go
// Before
args := []string{"run", "--rm", "-i", ...}
// After
args := []string{"run", "--rm", "-i", ...}
if server.DockerArgs != nil {
args = append(args, server.DockerArgs...)
}
```
### Security Considerations
1. **Allowlist approach**: Only allow specific safe arguments:
- `--network` (host, bridge, none)
- `--gpus`
- `--device`
- `--cap-add` / `--cap-drop`
- `--dns`
- `--shm-size`
2. **Blocklist dangerous args**:
- `--privileged` (too broad)
- `-v /:/host` (root filesystem access)
- `--pid host` (process namespace escape)
3. **Documentation**: Clearly document security implications of each allowed arg.
### Alternatives Considered
1. **Pre-defined profiles** (e.g., `profile: gpu`): Less flexible, requires predicting all use cases
2. **Separate fields** (e.g., `network: host`): Doesn't scale, adds complexity
3. **External compose file**: Over-engineered for simple args
### Testing
- [ ] Unit tests for arg parsing
- [ ] Integration test with `--network host`
- [ ] Security test: blocked args are rejected
- [ ] Backward compatibility: servers without `dockerArgs` work unchanged
### Related Issues
- Enables Chrome DevTools servers to work without workarounds
- Unblocks GPU-accelerated MCP servers
- Requested by community (link to any existing issues)
