Why is ports an array if we can only give one?

let service = new cloud.Service("pulumi-nginx", {
    containers: {
        nginx: {
            build: "./app",
            memory: 128,
            ports: [{ 
                port: 80, 
                protocol: 'http', 
                external: true 
            },
            { 
                port: 81, 
                protocol: 'http', 
                external: true 
            }],
        },
    },
    replicas: 1
});

" Error: Only one port can currently be exposed per Service."