nektos/act · error

network %q is specified multiple times

Error message

network %q is specified multiple times

What it means

In the advanced network notation (--network name=net1 with per-network options), each network endpoint is collected into a map keyed by target network name. If the same network target appears twice — e.g. '--network name=net1 --network name=net1' or overlapping long/short forms resolving to the same target — the duplicate key is rejected because Docker cannot attach one endpoint config twice.

Source

Thrown at pkg/container/docker_cli.go:798

		} else {
			hasNonUserDefined = true
		}
		if i == 0 {
			// The first network corresponds with what was previously the "only"
			// network, and what would be used when using the non-advanced syntax
			// `--network-alias`, `--link`, `--ip`, `--ip6`, and `--link-local-ip`
			// are set on this network, to preserve backward compatibility with
			// the non-advanced notation
			if err := applyContainerOptions(&n, copts); err != nil {
				return nil, err
			}
		}
		ep, err := parseNetworkAttachmentOpt(n)
		if err != nil {
			return nil, err
		}
		if _, ok := endpoints[n.Target]; ok {
			return nil, fmt.Errorf("network %q is specified multiple times", n.Target)
		}

		// For backward compatibility: if no custom options are provided for the network,
		// and only a single network is specified, omit the endpoint-configuration
		// on the client (the daemon will still create it when creating the container)
		if i == 0 && len(copts.netMode.Value()) == 1 {
			if ep == nil || reflect.ValueOf(*ep).IsZero() {
				continue
			}
		}
		endpoints[n.Target] = ep
	}
	if hasUserDefined && hasNonUserDefined {
		return nil, errors.New("conflicting options: cannot attach both user-defined and non-user-defined network-modes")
	}
	return endpoints, nil
}

View on GitHub (pinned to 4f41128141)

Solutions

1. Specify each network exactly once in options
2. If combining job-level container options and workflow-level options, deduplicate the --network entries
3. Use the advanced form only when you need per-network aliases/IPs, otherwise a single --network suffices

Example fix

# before
options: --network name=net1 --network name=net1

# after
options: --network name=net1

seen := map[string]bool{}
for _, n := range networks {
    if seen[n.Target] {
        return fmt.Errorf("network %q duplicated", n.Target)
    }
    seen[n.Target] = true
}

When it happens

Trigger: Passing the same network more than once via container options: combining a plain --network net1 with an advanced --network name=net1, or literally repeating the advanced form. Detected in act's local parse of container options.

Common situations: Workflow options strings concatenating fragments from multiple sources; migrating from single-network to advanced notation without removing the old flag; YAML anchors duplicating option lines.

Related errors

• network-scoped aliases are only supported for user-defined n
• %s is not a valid mac address
• invalid logging opts for driver %s
• --health-interval cannot be negative
• conflicting options: cannot specify both --mac-address and p

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/8dda876de133fc88. Report an issue: GitHub.