'Returns a list of container instances in a specified cluster.
:type cluster: string
:param cluster: The short name or full Amazon Resource Name (ARN) of
the cluster that hosts the container instances you want to list. If
you do not specify a cluster, the default cluster is assumed..
:type next_token: string
:param next_token: The `nextToken` value returned from a previous
paginated `ListContainerInstances` request where `maxResults` was
used and the results exceeded the value of that parameter.
Pagination continues from the end of the previous results that
returned the `nextToken` value. This value is `null` when there are
no more results to return.
:type max_results: integer
:param max_results: The maximum number of container instance results
returned by `ListContainerInstances` in paginated output. When this
parameter is used, `ListContainerInstances` only returns
`maxResults` results in a single page along with a `nextToken`
response element. The remaining results of the initial request can
be seen by sending another `ListContainerInstances` request with
the returned `nextToken` value. This value can be between 1 and
100. If this parameter is not used, then `ListContainerInstances`
returns up to 100 results and a `nextToken` value if applicable.'

def list_container_instances(self, cluster=None, next_token=None, max_results=None):

    params = {}
    if (cluster is not None):
        params['cluster'] = cluster
    if (next_token is not None):
        params['nextToken'] = next_token
    if (max_results is not None):
        params['maxResults'] = max_results
    return self._make_request(action='ListContainerInstances', verb='POST', path='/', params=params)
