Which Slack transport fits your deployment shape, and how Socket Mode behaves at runtime.

Choosing a transport

Socket Mode and HTTP Request URLs reach feature parity for messaging, slash commands, App Home, and interactivity. Pick by deployment shape, not features.

Concern Socket Mode (default) HTTP Request URLs
Public Gateway URL Not required Required (DNS, TLS, reverse proxy or tunnel)
Outbound network Outbound WSS to wss-primary.slack.com must be reachable No outbound WS; inbound HTTPS only
Tokens needed Bot identity: bot token + App-Level Token with connections:write; user identity: user token + App-Level Token Bot identity: bot token + Signing Secret; user identity: user token + Signing Secret
Dev laptop / behind firewall Works as-is Needs a public tunnel (ngrok, Cloudflare Tunnel, Tailscale Funnel) or staging Gateway
Horizontal scaling One Socket Mode session per app per host; multiple Gateways need separate Slack apps Stateless POST handler; multiple Gateway replicas can share one app behind a load balancer
Multi-account on one Gateway Supported; each account opens its own WS Supported; each account needs a unique webhookPath (default /slack/events) so registrations do not collide
Slash command transport Delivered over the WS connection; slash_commands[].url is ignored Slack POSTs to slash_commands[].url; field is required for the command to dispatch
Request signing Not used (auth is the App-Level Token) Slack signs every request; Apus verifies with signingSecret
Recovery on connection drop Slack SDK auto-reconnect is enabled; Apus also restarts failed Socket Mode sessions with bounded backoff. A fixed 15s client pong timeout applies. No persistent connection to drop; retries are per-request from Slack

Pick Socket Mode for single-Gateway hosts, dev laptops, and on-prem networks that can reach *.slack.com outbound but cannot accept inbound HTTPS.

Pick HTTP Request URLs when running multiple Gateway replicas behind a load balancer, when outbound WSS is blocked but inbound HTTPS is allowed, or when you already terminate Slack webhooks at a reverse proxy.

Slack can maintain multiple Socket Mode connections for one app and may deliver each payload to any connection. Separate Apus gateways that share a Slack app therefore need equivalent routing and authorization configuration. Otherwise, use a separate Slack app per gateway, a single relay ingress, or HTTP Request URLs behind a load balancer. See Using Socket Mode.

Relay mode

Relay mode separates Slack ingress from the Apus gateway. A trusted router owns the single Slack Socket Mode connection, chooses a destination gateway, and forwards a typed event over an authenticated websocket. The gateway still uses its own bot token for outbound Slack Web API calls.

{
  channels: {
    slack: {
      mode: "relay",
      botToken: { source: "env", provider: "default", id: "SLACK_BOT_TOKEN" },
      relay: {
        url: "wss://router.example.com/gateway/ws",
        authToken: { source: "env", provider: "default", id: "SLACK_RELAY_AUTH_TOKEN" },
        gatewayId: "team-gateway",
      },
    },
  },
}

The relay URL must use wss:// unless it targets localhost. Treat the bearer token and router route table as part of the Slack authorization boundary: routed events enter the normal Slack message handler as authorized activations. A router-provided slack_identity in the websocket hello frame can set the default outbound username and icon; an explicit identity supplied by the caller still wins. The relay connection reconnects with the same bounded backoff timing as Socket Mode and clears the router-provided identity whenever it disconnects.

Relay WebSocket connections honor the Gateway host's proxy environment (HTTPS_PROXY, HTTP_PROXY, ALL_PROXY, lowercase variants, and NO_PROXY). A wss:// relay uses an HTTP CONNECT tunnel when a proxy is configured. A matching NO_PROXY entry or a localhost ws:// URL connects directly. Proxy errors are reported instead of silently falling back to a direct relay connection.

Socket Mode transport tuning

Apus sets the Slack SDK client pong timeout to 15 seconds for Socket Mode. This is a fixed internal default and is not operator-configurable.

Notes: