def http(klass, url, interval, timeout=None, deregister=None, header=None):
        """
        Peform a HTTP GET against *url* every *interval* (e.g. "10s") to peform
        health check with an optional *timeout* and optional *deregister* after
        which a failing service will be automatically deregistered. Optional
        parameter *header* specifies headers sent in HTTP request. *header*
        paramater is in form of map of lists of strings,
        e.g. {"x-foo": ["bar", "baz"]}.
        """
        ret = {'http': url, 'interval': interval}
        if timeout:
            ret['timeout'] = timeout
        if deregister:
            ret['DeregisterCriticalServiceAfter'] = deregister
        if header:
            ret['header'] = header
        return ret
Peform a HTTP GET against *url* every *interval* (e.g. "10s") to peform
        health check with an optional *timeout* and optional *deregister* after
        which a failing service will be automatically deregistered. Optional
        parameter *header* specifies headers sent in HTTP request. *header*
        paramater is in form of map of lists of strings,
        e.g. {"x-foo": ["bar", "baz"]}.