Access IP address of Couchbase container on Docker Swarm cluster

Trying to run a Couchbase cluster on Docker Swarm cluster. After the cluster is started, I'd like to obtain the IP address of each Couchbase instance dynamically. docker inspect shows:

"NetworkSettings": {
        "Bridge": "",
        "SandboxID": "325807d55b552be3fe5b44b4d975c2486b3a56b320aa56fa0367e42348b82d64",
        "HairpinMode": false,
        "LinkLocalIPv6Address": "",
        "LinkLocalIPv6PrefixLen": 0,
        "Ports": {
            "11207/tcp": null,
            "11210/tcp": [
                {
                    "HostIp": "192.168.99.101",
                    "HostPort": "11210"
                }
            ],

Trying to access the IP address gives the error:

docker inspect --format '{{ .NetworkSettings.Ports.8091/tcp[0].HostIp }}' 922755302fef
Template parsing error: template: :1: unexpected ".8091" in operand; missing space?

What is the right format to access the IP address?

The property .NetworkSettings.Ports is a map, not a struct. You can use the index template function to access the map (and also slice) values:

$ docker inspect --format '{{ index .NetworkSettings.Ports "8091/tcp" 0 "HostIp" }}'

Note however, that this may not always return what you expect. If the container is configured to listen on all host interfaces, this will simply return 0.0.0.0. You could have a look at the networking feature that was introduced with Docker 1.9 for this without relying on looking up host IP addresses.