



                           GRID ASCII HELPER PROTOCOL
                         for Elastic Compute Cloud (EC2)
                                  VERSION 1.0


                                 Todd L Miller
                            [tlmiller@cs.wisc.edu]

                                 Febuary 2014

                               HTCondor Project
                    [http://research.cs.wisc.edu/htcondor]

                       Department of Computer Sciences
                       University of Wisconsin-Madison
                            1210 W. Dayton Street
                             Madison, WI  53706
                          [http://www.cs.wisc.edu]





1.    INTRODUCTION

    The object of the Grid ASCII Helper Protocol (GAHP) is to allow the
    use of the client library or package of a grid or cloud service via
    a simple ASCII-based protocol. A process which implements GAHP is
    referred to as a GAHP server. GAHP is designed to handle both
    synchronous (blocking) and asynchronous (non-blocking) calls.

    The first GAHP specification focused on the GRAM and GASS grid
    services of the Globus Toolkit. This GAHP specification focuses on
    the Google Compute Engine (GCE) cloud service.

1.1   WHY A GAHP?

    Although most grid and cloud services provide client libraries or
    modules in various languages that can be incorporated directly into
    applications that wish to use those services, there are several
    distinct advantages to using an independent GAHP server process
    instead. For instance, parts of the native API may provide only
    synchronous/blocking calls. Users who require a
    non-blocking/asynchronous interface must make use of multiple
    threads. Even if the native module is thread-safe, thread safety
    requires that _all_ modules linked into the process be both
    re-entrant and in agreement upon a threading model.
    This may be a significant barrier when trying to integrate the
    service client module into legacy non-thread-safe code, or when
    attempting to link with commercial libraries which either have no
    support for threads or define their own threading model. But because
    the GAHP server runs as a separate process, it can be easily
    implemented as a multi-threaded server, and still present an
    asynchronous non-blocking protocol. Worse yet, there may not be a
    client module available in the language of the application wishing
    to use the service. With a GAHP server, langauage choice is
    immaterial.

    GAHP facilitates the construction of multi-tier systems.  A first
    tier client can easily send ASCII commands via a socket (perhaps
    securely via an SSH or SSL tunnel) to a second tier running a GAHP
    server, allowing grid or cloud services to be consolidated at the
    second or third tier with minimal effort.

    Furthermore, GAHP, like many other simple ASCII-based protocols,
    supports the concept of component-based development independent of
    the software language used with minimal complexity. When a grid
    service has client modules available in multiple languages, those
    interfaces can look very different from each other. By using GAHP, a
    body of software could be written once with one interface and then
    subsequently utilize a GAHP server written in C, Java, or Perl --
    and said GAHP server could be running locally or as a daemon on a
    remote host.

1.2   AVAILABLE EC2 GAHP SERVERS

    The HTCondor Project at the University of Wisconsin-Madison has
    developed an EC2 GAHP server, written in C++, which uses pthreads and
    libcurl to support the EC2 protocol.  Many Unix platforms are
    supported.

    This GAHP is available as part of the HTCondor software distribution,
    version 7.7.0 or later.

2.0   GAHP SERVER IMPLEMENTATION

    GAHP itself, as a protocol, is independent of the underlying transport
    protocol and requires only a reliable ordered bi-directional data
    stream channel.

    A GAHP server, however, is assumed to read and respond to GAHP commands
    solely via stdin and stdout.  Should stdin to a GAHP server be closed,
    the GAHP server should immediately shutdown in a manner similar to the
    receipt of a QUIT command.  Therefore, a GAHP server can be easily
    invoked and managed via SSHD, inted, or rshd.  Software can spawn a
    local GAHP server via an interface such as POSIX.2 popen().

    Under no circumstances should a GAHP server block when issued any
    command.  All commands require a response nearly instantaneously.
    Therefore, most GAHP servers will be implemented as a multi-threaded
    process. Use of child processes or avoidance of blocking calls
    within the GAHP server are also options.

3.0   GAHP COMMANDS

    The following commands must be implemented by all GAHP servers:

        COMMANDS
        QUIT
        RESULTS
        VERSION

    The following commands may be implemented by any GAHP server:

        ASYNC_MODE_ON
        ASYNC_MODE_OFF
        RESPONSE_PREFIX

    The following commands are specific to EC2 and must be implemented
    by an EC2 GAHP server:

        EC2_VM_START
        EC2_VM_STOP
        EC2_VM_STATUS_ALL

        EC2_VM_CREATE_KEYPAIR
        EC2_VM_DESTROY_KEYPAIR

        EC2_VM_ASSOCIATE_ADDRESS
        EC2_VM_ATTACH_VOLUME
        EC2_VM_CREATE_TAGS
        EC2_VM_SERVER_TYPE

        EC2_VM_START_SPOT
        EC2_VM_STOP_SPOT
        EC2_VM_STATUS_SPOT
        EC2_VM_STATUS_ALL_SPOT

3.1   CONVENTIONS AND TERMS USED IN SECTION 3.2

    The following definitions are common to all GAHP protocol documents.

    <CRLF>

        The characters carriage return and line feed (in that
        order), _or_ solely the line feed character.

    <SP>

        The space character.

    line

        A sequence of ASCII characters ending with a <CRLF>.

    Request Line

        A request for action on the part of the GAHP server.

    Return Line

        A line immediately returned by the GAHP server upon
        receiving a Request Line.

    Result Line

        A line sent by the GAHP server in response to a RESULTS
        request, which communicates the results of a previous
        asynchronous command Request.

    S: and R:

        In the Example sections for the commands below, the prefix
        "S: " is used to signify what the client sends to the GAHP
        server.   The prefix "R: " is used to signify what the
        client receives from the GAHP server.  Note that the "S: "
        or "R: " should not actually be sent or received.

3.2   GAHP COMMAND STRUCTURE

    GAHP commands consist of three parts:

        * Request Line
        * Return Line
        * Result Line

    Each of these "Lines" consists of a variable length character
    string ending with the character sequence <CRLF>.

    A Request Line is a request from the client for action on the part of
    the GAHP server.  Each Request Line consists of a command code
    followed by argument field(s).  Command codes are a string of
    alphanumeric and underscore characters.  Upper and lower case
    alphabetic characters are to be treated identically with respect to
    command codes.  Thus, any of the following may represent the
    ASYNC_MODE_ON command:
        async_mode_on
        Async_Mode_On
        asYNc_MOde_oN
        ASYNC_MODE_ON
    In contrast, the argument fields of a Request Line are _case
    sensitive_.

    The Return Line is always generated by the server as an immediate
    response to a Request Line.  The first character of a Return Line will
    contain one of the following characters:
        S - for Success
        F - for Failure
        E - for a syntax or parse Error
    Any Request Line which contains an unrecognized or unsupported command,
    or a command with an insufficient number of arguments, will generate an
    "E" response.

    The Result Line is used to support commands that would otherwise
    block.  Any GAHP command which may require the implementation to block
    on network communication require a "request id" as part of the Request
    Line.  For such commands, the Result Line just communicates if the
    request has been successfully parsed and queued for service by the
    GAHP server.  At this point, the GAHP server would typically dispatch
    a new thread to actually service the request.  Once the request has
    completed, the dispatched thread should create a Result Line and
    enqueue it until the client issues a RESULT command.

3.3   TRANSPARENCY

    Arguments on a particular Line (be it Request, Return, or Result) are
    typically separated by a <SP>.  In the event that a string argument
    needs to contain a <SP> within the string itself, it must be escaped
    by placing a backslash ("\") in front of the <SP> character.  Thus,
    the character sequence "\ " (no quotes) must not be treated as a
    separator between arguments, but instead as a space character within a
    string argument. If a string argument contains a backslash
    character, it must be escaped by preceding it with another backslash
    character.

3.4   SEQUENCE OF EVENTS

    Upon startup, the GAHP server should output to stdout a banner string
    which is identical to the output from the VERSION command without the
    beginning "S " sequence (see example below).  Next, the GAHP server
    should wait for a complete Request Line from the client (from stdin).
    The server is to take no action until a Request Line sequence is
    received.

    There are no sequencing restrictions on the ordering of Requests in
    the GAHP API, even though some sequences may be semantically
    invalid for the underlying service. For example, attempting to
    stop a VM before starting it. The server shall not produce an "E" or
    "F" Return Line in the event of such sequences, but may produce a
    Result Line reflecting an error from the underlying service.

3.5   COMMAND SYNTAX

    This section contains the syntax for the Request, Return, and Result
    line for each command. The commands common to all GAHPs are defined
    first, followed by commands specific to the EC2 GAHP procotol.

3.5.1 COMMON GAHP COMMANDS

    These commands are common to all GAHP types.

    -----------------------------------------------

    COMMANDS

    List all the commands from this protocol specification which are
    implemented by this GAHP server.

    + Request Line:

        COMMANDS <CRLF>

    + Return Line:

        S <SP> <command 1> <SP> <command 2> <SP> ... <command X> <CRLF>

    + Result Line:

        None.

    -----------------------------------------------

    VERSION

    Return the version string for this GAHP.  The version string follows
    a specified format (see below).  Ideally, the version entire version
    string, including the starting and ending dollar sign ($)
    delimiters, should be a literal string in the text of the GAHP
    server executable.  This way, the Unix/RCS "ident" command can
    produce the version string.

    The version returned should correspond to the version of the
    protocol supported.

    + Request Line:

        VERSION <CRLF>

    + Return Line:

        S <SP> $GahpVesion: <SP> <major>.<minor>.<subminor> <SP>
            <build-month> <SP> <build-day-of-month> <SP>
            <build-year> <SP> <general-descrip> <SP>$ <CRLF>

        * major.minor.subminor = for this version of the
            protocol, use version x.y.z.

        * build-month = string with the month abbreviation when
            this GAHP server was built or released.  Permitted
            values are: "Jan", "Feb", "Mar", "Apr", "May", "Jun",
            "Jul", "Aug", "Sep", "Oct", "Nov", and "Dec".

        * build-day-of-month = day of the month when GAHP server
            was built or released; an integer between 1 and 31
            inclusive.

        * build-year = four digit integer specifying the year in
            which the GAHP server was built or released.

        * general-descrip = a string identifying a particular
            GAHP server implementation.

    + Result Line:

        None.

    + Example:

        S: VERSION
        R: S $GahpVersion: 1.0.0 Nov 26 2001 NCSA\ CoG\ Gahpd $

    -----------------------------------------------

    QUIT

    Free any/all system resources (close all sockets, etc) and terminate
    as quickly as possible.

    + Request Line:

        QUIT <CRLF>

    + Return Line:

        S <CRLF>

        Immediately afterwards, the command pipe should be closed
        and the GAHP server should terminate.

    + Result Line:

        None.

    -----------------------------------------------

    RESULTS

    Display all of the Result Lines which have been queued since the
    last RESULTS command was issued.  Upon success, the first return
    line specifies the number of subsequent Result Lines which will be
    displayed.  Then each result line appears (one per line) -- each
    starts with the request ID which corresponds to the request ID
    supplied when the corresponding command was submitted.  The exact
    format of the Result Line varies based upon which corresponding
    Request command was issued.

    IMPORTANT: Result Lines must be displayed in the _exact order_ in
    which they were queued!!!  In other words, the Result Lines
    displayed must be sorted in the order by which they were placed into
    the GAHP's result line queue, from earliest to most recent.

    + Request Line:

        RESULTS <CRLF>

    + Return Line(s):

        S <SP> <num-of-subsequent-result-lines> <CRLF>
        <reqid> <SP> ... <CRLF>
        <reqid> <SP> ... <CRLF>
        ...

        * reqid = integer Request ID, set to the value specified in
            the corresponding Request Line.

    + Result Line:

        None.

    + Example:

        S: RESULTS
        R: S 1
        R: 100 0

    -----------------------------------------------

    ASYNC_MODE_ON

    Enable Asynchronous notification when the GAHP server has results
    pending for a client. This is most useful for clients that do not
    want to periodically poll the GAHP server with a RESULTS command.
    When asynchronous notification mode is active, the GAHP server will
    print out an 'R' (without the quotes) on column one when the
    'RESULTS' command would return one or more lines. The 'R' is printed
    only once between successive 'RESULTS' commands.    The 'R' is
    also guaranteed to only appear in between atomic return lines; the
    'R" will not interrupt another command's output.

    If there are already pending results when the asynchronous results
    available mode is activated, no indication of the presence of those
    results will be given. A GAHP server is permitted to only consider
    changes to it's result queue for additions after the ASYNC_MODE_ON
    command has successfully completed. GAHP clients should issue a
    'RESULTS' command immediately after enabling asynchronous
    notification, to ensure that any results that may have been added to
    the queue during the processing of the ASYNC_MODE_ON command are
    accounted for.

    + Request Line:

        ASYNC_MODE_ON <CRLF>

    + Return Line:

        S <CRLF>

        Immediately afterwards, the client should be prepared to
        handle an R <CRLF> appearing in the output of the GAHP
        server.

    + Result Line:

        None.

    + Example:

        S: ASYNC_MODE_ON
        R: S
        S: GRAM_PING 00001 beak.cs.wisc.edu/jobmanager
        R: S
        S: GRAM_PING 00002 nostos.cs.wisc.edu/jobmanager
        R: S
        R: R
        S: RESULTS
        R: S 2
        R: 00001 0
        R: 00002 0

    Note that you are NOT guaranteed that the 'R' will not appear
    between the dispatching of a command and the return line(s) of that
    command; the GAHP server only guarantees that the 'R' will not
    interrupt an in-progress return. The following is also a legal
    example:
        S: ASYNC_MODE_ON
        R: S
        S: GRAM_PING 00001 beak.cs.wisc.edu/jobmanager
        R: S
        S: GRAM_PING 00002 nostos.cs.wisc.edu/jobmanager
        R: R
        R: S
        S: RESULTS
        R: S 2
        R: 00001 0
        R: 00002 0

        (Note the reversal of the R and the S after GRAM_PING 00002)

    -----------------------------------------------

    ASYNC_MODE_OFF

    Disable asynchronous results-available notification. In this mode,
    the only way to discover available results is to poll with the
    RESULTS command.  This mode is the default. Asynchronous mode can be
    enable with the ASYNC_MODE_ON command.

    + Request Line:

        ASYNC_MODE_OFF <CRLF>

    + Return Line:

        S <CRLF>

    + Result Line:

        None

    + Example:

        S: ASYNC_MODE_OFF
        R: S

    -----------------------------------------------

    RESPONSE_PREFIX

    Specify a prefix that the GAHP server should use to prepend every
    subsequent line of output. This may simplify parsing the output of
    the GAHP server by the client program, especially in cases where the
    responses of more one GAHP server are "collated" together.

    This affects the output of both return lines and result lines for all
    subsequent commands (NOT including this one).

    + Request Line:

        RESPONSE_PREFIX <SP> <prefix> <CRLF>

        <prefix> = an arbitrary string of characters which you want to
        prefix every subsequent line printed by the GAHP server.

    + Return Line:

        S <CRLF>

    + Result Line:

        None.

    + Example:

        S: RESPONSE_PREFIX GAHP:
        R: S
        S: RESULTS
        R: GAHP:S 0
        S: RESPONSE_PREFIX NEW_PREFIX_
        R: GAHP:S
        S: RESULTS
        R: NEW_PREFIX_S 0

    -----------------------------------------------

3.5.2 GAHP COMMANDS SPECIFIC TO EC2

    The following commands are specific to the EC2 GAHP. All commands
    will include the following arguments.

    * request-ID    = a non-zero Request ID
    * service-URL   = the URL used to access the EC2 service's RESTful API
    * accessKeyFile = the full path to a file containing nothing but the
                      EC2 access key (and an optional trailing newline)
    * secretKeyFile = the full path to a file containing nothing but the
                      EC2 secret key (and an optional trailing newline)

    We do not directly specify keys to minimize the chance of interception.

    Required values must not be the literal string "NULL" (without the
    quotes), as this denotes that the corresponding attribute was not set.
    If an optional value is not set, it _must_ be represented in this way.

    The following is the Return Line for all EC2 GAHP commands unless
    otherwise specified.

    + Return Line:

        <result> <CRLF>

        * result             = the character "S" (without the quotes) for
                               the successful submission of the request
                               (meaning the request is now pending), or an
                               "E" (without the quotes) for an error
                               parsing the request or its arguments (e.g.
                               an unrecognized or unsupported command, or
                               missing or malformed arguments)

    The following is the Result Line for all EC2 GAHP commands unless
    otherwise specified.

    + Result Line:

        One of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>
        <request-ID> <SP> 0 <CRLF>

        * error-code         = a fixed string denoting the type of error
        * error-string       = a variable string with more detail

    The definitions for error-code and error-string are identical for every
    Result Line unless otherwise stated.

    -----------------------------------------------

    EC2_VM_START

    Start an instance of the specified VM.

    + Request Line:

        EC2_VM_START <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <image-ID> <SP> <ssh-keypair-name>
            <SP> <user-data-string> <SP> <user-data-file>
            <SP> <instance-type> <SP> <availability-zone>
            <SP> <subnet-ID> <SP> <private-ip-address>
            <SP> <client-token> [<SP> <security-group>]+ <CRLF>

        The following attributes are required.

        * image-ID           = an existing AMI ID (or equivalent)

        The following are optional.

        * ssh-keypair-name   = an existing SSH keypair name
        * user-data-string   = a string supplied by the user, in which
                               spaces must be escaped (see above)
        * user-data-file     = the full path to a file containing nothing
                               but the (unencoded) user data.  Appended to
                               user-data-string, if both are set.
        * instance-type      = the instance type
        * availability-zone  = the availability zone
        * subnet-ID          = the subnet ID
        * private-ip-address = the private IP address of the instance
        * client-token       = the client token

        The following attribute(s) may be omitted.

        * security-group     = a security group.

        Security groups are passed to the service unmodified.  The client
        may specify an arbitrary number of security group strings, including
        zero.  (Services may limit the number of security groups for an
        instance, but the EC2 GAHP does not.)

    + Result Line:

        Either of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 0 <SP> <instance-ID> <CRLF>
        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>

        * request-ID         = from the corresponding Request Line
        * instance-ID        = the ID of the started instance

    -----------------------------------------------

    EC2_VM_STOP

    Stop ("terminate") the specified VM instance.

    + Request Line:

        EC2_VM_STOP <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <instance-ID> <CRLF>

        The following attributes are required.

        * instance-ID           = an instance ID (such as may have been
                                  returned by EC2_VM_START, although this is
                                  not required)

    -----------------------------------------------

    EC2_VM_STATUS_ALL

    Discover the status of all instances the given credentials can observe.
    This may include instances not started by the GAHP; the client must
    maintain its own list of instances if it cares.  This does _not_ include
    spot instances; see EC2_VM_STATUS_SPOT and EC2_VM_STATUS_ALL_SPOT.

    + Request Line:

        EC2_VM_STATUS_ALL <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile> <CRLF>

    + Result Line:

        One of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>
        <request-ID> <SP> 0
                        [<SP> <instance-ID> <SP> <status>
                         <SP> [<client-token>] <SP> [<ssh-keypair-name>]
                         <SP> [<state-reason-code>] <SP> [<public-dns-name>]
                        ]* <CRLF>

        * request-ID         = from the corresponding Request Line

        A success returns 0 or more 6-tuples, the last four values of which
        may be the literal string "NULL" (without the quotes) to denote that
        the corresponding attribute was not set.  The six attributes are:

        * instance-ID       = an instance ID
        * status            = the status of the preceding instance
        * client-token      = the client token, if any
        * ssh-keypair-name  = the SSH keypair name, if any
        * state-reason-code = the state reason code, if any
        * public-dns-name   = the public DNS name, if any

    -----------------------------------------------

    EC2_VM_CREATE_KEYPAIR

    Generate and register an SSH keypair on the service.

    + Request Line:

        EC2_VM_CREATE_KEYPAIR <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <ssh-keypair-name> <SP> <private-key-file> <CRLF>

        * ssh-keypair-name  = register the generated keypair with this name
        * private-key-file  = the full path to the file to which to write
                              the private key half of the generated keypair

    -----------------------------------------------

    EC2_VM_DESTROY_KEYPAIR

    Remove the named SSH keypair from the service.

    + Request Line:

        EC2_VM_DESTROY_KEYPAIR <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <ssh-keypair-name> <CRLF>

        * ssh-keypair-name  = delete the keypair named this

    -----------------------------------------------

    EC2_VM_ASSOCIATE_ADDRESS

    Associate the given Elastic IP with the given instance.  Accepts
    both EC2 and VPC -style Elastic IP specifiers.

    + Request Line:

        EC2_VM_ASSOCIATE_ADDRESS <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <instance-ID> <SP> <elastic-IP> <CRLF>

        * instance-ID       = an instance ID
        * elastic-IP        = an Elastic IP specifier

    -----------------------------------------------

    EC2_VM_ATTACH_VOLUME

    Attach an EBS volume to an instance.

    + Request Line:

        EC2_VM_ATTACH_VOLUME <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <volume-ID> <SP> <instance-ID>
            <SP> <device> <CRLF>

        * volume-ID         = an EBS volume ID
        * instance-ID       = an instance ID
        * device            = which device to attach the volume as

    -----------------------------------------------

    EC2_VM_CREATE_TAGS

    Add the specified tags to the given resource.

    + Request Line:

        EC2_VM_CREATE_TAGS <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <resource-ID> [<SP> <tag-name> = <tag-value>]+ CRLF

        * resource-ID       = a resource ID (usually an instance ID)

        The following two attributes must be specified as a pair separated
        by a literal "=" (no quotes) but no spaces; escaped spaces will be
        treated as part of the tag-name or tag-value, depending on which
        side of the "=" they're on.  At least one pair must be present. The
        EC2 GAHP does not specify a maximum number of pairs.

        * tag-name          = the name of the tag to add
        * tag-value         = the value of the tag to add

    -----------------------------------------------

    EC2_VM_SERVER_TYPE

    Determine the type of the EC2 service offered at the given URL.

    + Request Line:

        EC2_VM_SERVER_TYPE <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile> <CRLF>

    + Result Line:

        One of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>
        <request-ID> <SP> 0 <SP> <server-type> <CRLF>

        * server-type       = one of "Unknown", "Amazon", "OpenStack",
                              "Nimbus", or "Eucalyptus" (without the quotes)

    -----------------------------------------------

    EC2_VM_START_SPOT

    Request a Spot instance.

    + Request Line:

        EC2_VM_START_SPOT <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <image-ID> <SP> <spot-price>
            <SP> <ssh-keypair-name>
            <SP> <user-data-string> <SP> <user-data-file>
            <SP> <instance-type> <SP> <availability-zone>
            <SP> <subnet-ID> <SP> <private-ip-address>
            <SP> <client-token> [<SP> <security-group]+ <CRLF>

        The following attributes are required.

        * image-ID           = an existing AMI ID (or equivalent)
        * spot-price         = a string specifying the bid ("0.0022")

        The remainder of this command's specification is identical to
        EC2_VM_START.

    + Result Line:

        Either of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 0 <SP> <spot-instance-ID> <CRLF>
        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>

        * request-ID         = from the corresponding Request Line
        * spot-instance-ID   = the ID of the Spot instance request

    -----------------------------------------------

    EC2_VM_STOP_SPOT

    Stop ("cancel") a spot request.

    + Request Line:

        EC2_VM_STOP_SPOT <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <spot-instance-ID> <CRLF>

    -----------------------------------------------

    EC2_VM_STATUS_SPOT

    Determine the status of the given Spot instance request.  This function
    is _deprecated_, and should not be used; EC2_VM_STATUS_SPOT_ALL returns
    the same information, but more efficiently.

    + Request Line:

        EC2_VM_STATUS_SPOT <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile>
            <SP> <spot-instance-ID> <CRLF>

    + Result Line:

        Any of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 0 <CRLF>
        <request-ID> <SP> 0 <SP> <spot-instance-ID> <SP> <state>
                     <SP> <client-token>
                     <SP> [<instance-ID>] <SP> [<status-code>] <CRLF>
        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>

        The shorter succes line indicates that no spot instance request
        with the given ID was found (but the search completed succesfully).

        * request-ID         = from the corresponding Request Line
        * spot-instance-ID   = the ID of the Spot instance request
        * state              = the state of the Spot instance request
        * client-token       = the client token supplied in the request

        The following two attributes may be the literal string "NULL"
        (without the quotes) to denote that the corresponding attribute
        was not set:

        * instance-ID        = ID of the instance spawned by this request
        * status-code        = the status code of the request

    -----------------------------------------------

    EC2_VM_STATUS_ALL_SPOT

    Obtain status information about all the spot instance requests visible
    to the given credentials.

    + Request Line:

        EC2_VM_STATUS_ALL_SPOT <SP> <request-ID> <SP> <service-URL>
            <SP> <accessKeyFile> <SP> <secretKeyFile> <CRLF>

    + Result Line:

        Either of the following, where 0 is success and 1 is failure.

        <request-ID> <SP> 0 [<SP> <spot-instance-ID> <SP> <state>
                     <SP> <client-token>
                     <SP> [<instance-ID>] <SP> [<status-code>]]* <CRLF>
        <request-ID> <SP> 1 <SP> <error-code> <SP> <error-string> <CRLF>

        * request-ID         = from the corresponding Request Line

        A success returns 0 or more 5-tuples, the last two values of which
        may be the literal string "NULL" (without the quotes) to denote that
        the corresponding attribute was not set.  The five attributes are:

        * spot-instance-ID   = the ID of the Spot instance request
        * state              = the state of the Spot instance request
        * client-token       = the client token supplied in the request
        * instance-ID        = ID of the instance spawned by this request
        * status-code        = the status code of the request
