mesos.proto

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package mesos;

option java_package = "org.apache.mesos";
option java_outer_classname = "Protos";


/**
 * Status is used to indicate the state of the scheduler and executor
 * driver after function calls.
 */
enum Status {
  DRIVER_NOT_STARTED = 1;
  DRIVER_RUNNING = 2;
  DRIVER_ABORTED = 3;
  DRIVER_STOPPED = 4;
}


/**
 * A unique ID assigned to a framework. A framework can reuse this ID
 * in order to do failover (see MesosSchedulerDriver).
 */
message FrameworkID {
  required string value = 1;
}


/**
 * A unique ID assigned to an offer.
 */
message OfferID {
  required string value = 1;
}


/**
 * A unique ID assigned to a slave. Currently, a slave gets a new ID
 * whenever it (re)registers with Mesos. Framework writers shouldn't
 * assume any binding between a slave ID and and a hostname.
 */
message SlaveID {
  required string value = 1;
}


/**
 * A framework generated ID to distinguish a task. The ID must remain
 * unique while the task is active. However, a framework can reuse an
 * ID _only_ if a previous task with the same ID has reached a
 * terminal state (e.g., TASK_FINISHED, TASK_LOST, TASK_KILLED, etc.).
 */
message TaskID {
  required string value = 1;
}


/**
 * A framework generated ID to distinguish an executor. Only one
 * executor with the same ID can be active on the same slave at a
 * time.
 */
message ExecutorID {
  required string value = 1;
}


/**
 * A slave generated ID to distinguish a container. The ID must be unique
 * between any active or completed containers on the slave. In particular,
 * containers for different runs of the same (framework, executor) pair must be
 * unique.
 */
message ContainerID {
  required string value = 1;
}


/**
 * Describes a framework. The user field is used to determine the
 * Unix user that an executor/task should be launched as. If the user
 * field is set to an empty string Mesos will automagically set it
 * to the current user. Note that the ID is only available after a
 * framework has registered, however, it is included here in order to
 * facilitate scheduler failover (i.e., if it is set then the
 * MesosSchedulerDriver expects the scheduler is performing failover).
 * The amount of time that the master will wait for the scheduler to
 * failover before removing the framework is specified by
 * failover_timeout. If checkpoint is set, framework pid, executor
 * pids and status updates are checkpointed to disk by the slaves.
 * Checkpointing allows a restarted slave to reconnect with old
 * executors and recover status updates, at the cost of disk I/O.
 * The role field is used to group frameworks for allocation
 * decisions, depending on the allocation policy being used.
 * If the hostname field is set to an empty string Mesos will
 * automagically set it to the current hostname.
 * The principal field should match the credential the framework uses
 * in authentication. This field is used for framework API rate
 * exporting and limiting and should be set even if authentication is
 * not enabled if these features are desired.
 */
message FrameworkInfo {
  required string user = 1;
  required string name = 2;
  optional FrameworkID id = 3;
  optional double failover_timeout = 4 [default = 0.0];
  optional bool checkpoint = 5 [default = false];
  optional string role = 6 [default = "*"];
  optional string hostname = 7;
  optional string principal = 8;
}


/**
 * Describes a health check for a task or executor (or any arbitrary
 * process/command). A "strategy" is picked by specifying one of the
 * optional fields, currently only 'http' and 'command' are
 * supported. Specifying more than one strategy is an error.
 */
message HealthCheck {
  // Describes an HTTP health check.
  message HTTP {
    // Port to send the HTTP request.
    required uint32 port = 1;

    // HTTP request path.
    optional string path = 2 [default = "/"];

    // TODO(benh): Implement:
    // Whether or not to use HTTPS.
    // optional bool ssl = 3 [default = false];

    // Expected response statuses. Not specifying any statuses implies
    // that any returned status is acceptable.
    repeated uint32 statuses = 4;

    // TODO(benh): Include an 'optional bytes data' field for checking
    // for specific data in the response.
  }

  optional HTTP http = 1;

  // TODO(benh): Consider adding a URL health check strategy which
  // allows doing something similar to the HTTP strategy but
  // encapsulates all the details in a single string field.

  // TODO(benh): Other possible health check strategies could include
  // one for TCP/UDP or a "command". A "command" could be running a
  // (shell) command to check the healthiness. We'd need to determine
  // what arguments (or environment variables) we'd want to set so
  // that the command could do it's job (i.e., do we want to expose
  // the stdout/stderr and/or the pid to make checking for healthiness
  // easier).

  // Amount of time to wait until starting the health checks.
  optional double delay_seconds = 2 [default = 15.0];

  // Interval between health checks.
  optional double interval_seconds = 3 [default = 10.0];

  // Amount of time to wait for the health check to complete.
  optional double timeout_seconds = 4 [default = 20.0];

  // Number of consecutive failures until considered unhealthy.
  optional uint32 consecutive_failures = 5 [default = 3];

  // Amount of time to allow failed health checks since launch.
  optional double grace_period_seconds = 6 [default = 10.0];

  // Command health check.
  optional CommandInfo command = 7;
}


/**
 * Describes a command, executed via: '/bin/sh -c value'. Any URIs specified
 * are fetched before executing the command.  If the executable field for an
 * uri is set, executable file permission is set on the downloaded file.
 * Otherwise, if the downloaded file has a recognized archive extension
 * (currently [compressed] tar and zip) it is extracted into the executor's
 * working directory. This extraction can be disabled by setting `extract` to
 * false. In addition, any environment variables are set before executing
 * the command (so they can be used to "parameterize" your command).
 */
message CommandInfo {
  message URI {
    required string value = 1;
    optional bool executable = 2;
    optional bool extract = 3 [default = true];
  }

  // Describes a container.
  // Not all containerizers currently implement ContainerInfo, so it
  // is possible that a launched task will fail due to supplying this
  // attribute.
  // NOTE: The containerizer API is currently in an early beta or
  // even alpha state. Some details, like the exact semantics of an
  // "image" or "options" are not yet hardened.
  // TODO(tillt): Describe the exact scheme and semantics of "image"
  // and "options".
  message ContainerInfo {
    // URI describing the container image name.
    required string image = 1;

    // Describes additional options passed to the containerizer.
    repeated string options = 2;
  }

  // NOTE: MesosContainerizer does currently not support this
  // attribute and tasks supplying a 'container' will fail.
  optional ContainerInfo container = 4;

  repeated URI uris = 1;

  optional Environment environment = 2;

  // There are two ways to specify the command:
  // 1) If 'shell == true', the command will be launched via shell
  //		(i.e., /bin/sh -c 'value'). The 'value' specified will be
  //		treated as the shell command. The 'arguments' will be ignored.
  // 2) If 'shell == false', the command will be launched by passing
  //		arguments to an executable. The 'value' specified will be
  //		treated as the filename of the executable. The 'arguments'
  //		will be treated as the arguments to the executable. This is
  //		similar to how POSIX exec families launch processes (i.e.,
  //		execlp(value, arguments(0), arguments(1), ...)).
  // NOTE: The field 'value' is changed from 'required' to 'optional'
  // in 0.20.0. It will only cause issues if a new framework is
  // connecting to an old master.
  optional bool shell = 6 [default = true];
  optional string value = 3;
  repeated string arguments = 7;

  // Enables executor and tasks to run as a specific user. If the user
  // field is present both in FrameworkInfo and here, the CommandInfo
  // user value takes precedence.
  optional string user = 5;
}


/**
 * Describes information about an executor. The 'data' field can be
 * used to pass arbitrary bytes to an executor.
 */
message ExecutorInfo {
  required ExecutorID executor_id = 1;
  optional FrameworkID framework_id = 8; // TODO(benh): Make this required.
  required CommandInfo command = 7;
  // Executor provided with a container will launch the container
  // with the executor's CommandInfo and we expect the container to
  // act as a Mesos executor.
  optional ContainerInfo container = 11;
  repeated Resource resources = 5;
  optional string name = 9;

  // Source is an identifier style string used by frameworks to track
  // the source of an executor. This is useful when it's possible for
  // different executor ids to be related semantically.
  // NOTE: Source is exposed alongside the resource usage of the
  // executor via JSON on the slave. This allows users to import
  // usage information into a time series database for monitoring.
  optional string source = 10;
  optional bytes data = 4;
}


/**
 * Describes a master. This will probably have more fields in the
 * future which might be used, for example, to link a framework webui
 * to a master webui.
 */
message MasterInfo {
  required string id = 1;
  required uint32 ip = 2;
  required uint32 port = 3 [default = 5050];
  optional string pid = 4;
  optional string hostname = 5;
}


/**
 * Describes a slave. Note that the 'id' field is only available after
 * a slave is registered with the master, and is made available here
 * to facilitate re-registration.  If checkpoint is set, the slave is
 * checkpointing its own information and potentially frameworks'
 * information (if a framework has checkpointing enabled).
 */
message SlaveInfo {
  required string hostname = 1;
  optional int32 port = 8 [default = 5051];
  repeated Resource resources = 3;
  repeated Attribute attributes = 5;
  optional SlaveID id = 6;
  optional bool checkpoint = 7 [default = false];

  // Deprecated!
  optional string webui_hostname = 2;
  optional int32 webui_port = 4 [default = 8081];
}


/**
 * Describes an Attribute or Resource "value". A value is described
 * using the standard protocol buffer "union" trick.
 */
message Value {
  enum Type {
    SCALAR = 0;
    RANGES = 1;
    SET = 2;
    TEXT = 3;
  }

  message Scalar {
    required double value = 1;
  }

  message Range {
    required uint64 begin = 1;
    required uint64 end = 2;
  }

  message Ranges {
    repeated Range range = 1;
  }

  message Set {
    repeated string item = 1;
  }

  message Text {
    required string value = 1;
  }

  required Type type = 1;
  optional Scalar scalar = 2;
  optional Ranges ranges = 3;
  optional Set set = 4;
  optional Text text = 5;
}


/**
 * Describes an attribute that can be set on a machine. For now,
 * attributes and resources share the same "value" type, but this may
 * change in the future and attributes may only be string based.
 */
message Attribute {
  required string name = 1;
  required Value.Type type = 2;
  optional Value.Scalar scalar = 3;
  optional Value.Ranges ranges = 4;
  optional Value.Set set = 6;
  optional Value.Text text = 5;
}


/**
 * Describes a resource on a machine. A resource can take on one of
 * three types: scalar (double), a list of finite and discrete ranges
 * (e.g., [1-10, 20-30]), or a set of items. A resource is described
 * using the standard protocol buffer "union" trick.
 *
 * TODO(benh): Add better support for "expected" resources (e.g.,
 * cpus, memory, disk, network).
 */
message Resource {
  required string name = 1;
  required Value.Type type = 2;
  optional Value.Scalar scalar = 3;
  optional Value.Ranges ranges = 4;
  optional Value.Set set = 5;
  optional string role = 6 [default = "*"];
}


/*
 * A snapshot of resource usage statistics.
 */
message ResourceStatistics {
  required double timestamp = 1; // Snapshot time, in seconds since the Epoch.

  // CPU Usage Information:
  // Total CPU time spent in user mode, and kernel mode.
  optional double cpus_user_time_secs = 2;
  optional double cpus_system_time_secs = 3;

  // Number of CPUs allocated.
  optional double cpus_limit = 4;

  // cpu.stat on process throttling (for contention issues).
  optional uint32 cpus_nr_periods = 7;
  optional uint32 cpus_nr_throttled = 8;
  optional double cpus_throttled_time_secs = 9;

  // Memory Usage Information:
  optional uint64 mem_rss_bytes = 5; // Resident Set Size.

  // Amount of memory resources allocated.
  optional uint64 mem_limit_bytes = 6;

  // Broken out memory usage information (files, anonymous, and mmaped files)
  optional uint64 mem_file_bytes = 10;
  optional uint64 mem_anon_bytes = 11;
  optional uint64 mem_mapped_file_bytes = 12;

  // TODO(bmahler): Add disk usage.

  // Perf statistics.
  optional PerfStatistics perf = 13;

  // Network Usage Information:
  optional uint64 net_rx_packets = 14;
  optional uint64 net_rx_bytes = 15;
  optional uint64 net_rx_errors = 16;
  optional uint64 net_rx_dropped = 17;
  optional uint64 net_tx_packets = 18;
  optional uint64 net_tx_bytes = 19;
  optional uint64 net_tx_errors = 20;
  optional uint64 net_tx_dropped = 21;
}


/**
 * Describes a snapshot of the resource usage for an executor.
 *
 * TODO(bmahler): Note that we want to be sending this information
 * to the master, and subsequently to the relevant scheduler. So
 * this proto is designed to be easy for the scheduler to use, this
 * is why we provide the slave id, executor info / task info.
 */
message ResourceUsage {
  required SlaveID slave_id = 1;
  required FrameworkID framework_id = 2;

  // Resource usage is for an executor. For tasks launched with
  // an explicit executor, the executor id is provided. For tasks
  // launched without an executor, our internal executor will be
  // used. In this case, we provide the task id here instead, in
  // order to make this message easier for schedulers to work with.

  optional ExecutorID executor_id = 3; // If present, this executor was
  optional string executor_name = 4;   // explicitly specified.

  optional TaskID task_id = 5; // If present, the task did not have an executor.

  // If missing, the isolation module cannot provide resource usage.
  optional ResourceStatistics statistics = 6;
}


/**
 * Describes a sample of events from "perf stat". Only available on
 * Linux.
 *
 * NOTE: Each optional field matches the name of a perf event (see
 * "perf list") with the following changes:
 * 1. Names are downcased.
 * 2. Hyphens ('-') are replaced with underscores ('_').
 * 3. Events with alternate names use the name "perf stat" returns,
 *    e.g., for the event "cycles OR cpu-cycles" perf always returns
 *    cycles.
 */
message PerfStatistics {
  required double timestamp = 1; // Start of sample interval, in seconds since the Epoch.
  required double duration = 2;  // Duration of sample interval, in seconds.

  // Hardware event.
  optional uint64 cycles = 3;
  optional uint64 stalled_cycles_frontend = 4;
  optional uint64 stalled_cycles_backend = 5;
  optional uint64 instructions = 6;
  optional uint64 cache_references = 7;
  optional uint64 cache_misses = 8;
  optional uint64 branches = 9;
  optional uint64 branch_misses = 10;
  optional uint64 bus_cycles = 11;
  optional uint64 ref_cycles = 12;

  // Software event.
  optional double cpu_clock = 13;
  optional double task_clock = 14;
  optional uint64 page_faults = 15;
  optional uint64 minor_faults = 16;
  optional uint64 major_faults = 17;
  optional uint64 context_switches = 18;
  optional uint64 cpu_migrations = 19;
  optional uint64 alignment_faults = 20;
  optional uint64 emulation_faults = 21;

  // Hardware cache event.
  optional uint64 l1_dcache_loads = 22;
  optional uint64 l1_dcache_load_misses = 23;
  optional uint64 l1_dcache_stores = 24;
  optional uint64 l1_dcache_store_misses = 25;
  optional uint64 l1_dcache_prefetches = 26;
  optional uint64 l1_dcache_prefetch_misses = 27;
  optional uint64 l1_icache_loads = 28;
  optional uint64 l1_icache_load_misses = 29;
  optional uint64 l1_icache_prefetches = 30;
  optional uint64 l1_icache_prefetch_misses = 31;
  optional uint64 llc_loads = 32;
  optional uint64 llc_load_misses = 33;
  optional uint64 llc_stores = 34;
  optional uint64 llc_store_misses = 35;
  optional uint64 llc_prefetches = 36;
  optional uint64 llc_prefetch_misses = 37;
  optional uint64 dtlb_loads = 38;
  optional uint64 dtlb_load_misses = 39;
  optional uint64 dtlb_stores = 40;
  optional uint64 dtlb_store_misses = 41;
  optional uint64 dtlb_prefetches = 42;
  optional uint64 dtlb_prefetch_misses = 43;
  optional uint64 itlb_loads = 44;
  optional uint64 itlb_load_misses = 45;
  optional uint64 branch_loads = 46;
  optional uint64 branch_load_misses = 47;
  optional uint64 node_loads = 48;
  optional uint64 node_load_misses = 49;
  optional uint64 node_stores = 50;
  optional uint64 node_store_misses = 51;
  optional uint64 node_prefetches = 52;
  optional uint64 node_prefetch_misses = 53;
}


/**
 * Describes a request for resources that can be used by a framework
 * to proactively influence the allocator.  If 'slave_id' is provided
 * then this request is assumed to only apply to resources on that
 * slave.
 */
message Request {
  optional SlaveID slave_id = 1;
  repeated Resource resources = 2;
}


/**
 * Describes some resources available on a slave. An offer only
 * contains resources from a single slave.
 */
message Offer {
  required OfferID id = 1;
  required FrameworkID framework_id = 2;
  required SlaveID slave_id = 3;
  required string hostname = 4;
  repeated Resource resources = 5;
  repeated Attribute attributes = 7;
  repeated ExecutorID executor_ids = 6;
}


/**
 * Describes a task. Passed from the scheduler all the way to an
 * executor (see SchedulerDriver::launchTasks and
 * Executor::launchTask). Either ExecutorInfo or CommandInfo should be set.
 * A different executor can be used to launch this task, and subsequent tasks
 * meant for the same executor can reuse the same ExecutorInfo struct.
 */
message TaskInfo {
  required string name = 1;
  required TaskID task_id = 2;
  required SlaveID slave_id = 3;
  repeated Resource resources = 4;
  optional ExecutorInfo executor = 5;
  optional CommandInfo command = 7;
  // Task provided with a container will launch the container as part
  // of this task paired with the task's CommandInfo.
  optional ContainerInfo container = 9;
  optional bytes data = 6;
  // A health check for the task (currently in *alpha* and initial
  // support will only be for TaskInfo's that have a CommandInfo).
  optional HealthCheck health_check = 8;
}


/**
 * Describes possible task states. IMPORTANT: Mesos assumes tasks that
 * enter terminal states (see below) imply the task is no longer
 * running and thus clean up any thing associated with the task
 * (ultimately offering any resources being consumed by that task to
 * another task).
 */
enum TaskState {
  TASK_STAGING = 6;  // Initial state. Framework status updates should not use.
  TASK_STARTING = 0;
  TASK_RUNNING = 1;
  TASK_FINISHED = 2; // TERMINAL.
  TASK_FAILED = 3;   // TERMINAL.
  TASK_KILLED = 4;   // TERMINAL.
  TASK_LOST = 5;     // TERMINAL.

  // TODO(benh): TASK_ERROR = 7; // TERMINAL.
}


/**
 * Describes the current status of a task.
 */
message TaskStatus {
  required TaskID task_id = 1;
  required TaskState state = 2;
  optional string message = 4; // Possible message explaining state.
  optional bytes data = 3;
  optional SlaveID slave_id = 5;
  optional ExecutorID executor_id = 7; // TODO(benh): Use in master/slave.
  optional double timestamp = 6;

  // Describes whether the task has been determined to be healthy
  // (true) or unhealthy (false) according to the HealthCheck field in
  // the command info.
  optional bool healthy = 8;
}


/**
 * Describes possible filters that can be applied to unused resources
 * (see SchedulerDriver::launchTasks) to influence the allocator.
 */
message Filters {
  // Time to consider unused resources refused. Note that all unused
  // resources will be considered refused and use the default value
  // (below) regardless of whether Filters was passed to
  // SchedulerDriver::launchTasks. You MUST pass Filters with this
  // field set to change this behavior (i.e., get another offer which
  // includes unused resources sooner or later than the default).
  optional double refuse_seconds = 1 [default = 5.0];
}


/**
* Describes a collection of environment variables. This is used with
* CommandInfo in order to set environment variables before running a
* command.
*/
message Environment {
  message Variable {
    required string name = 1;
    required string value = 2;
  }

  repeated Variable variables = 1;
}


/**
 * A generic (key, value) pair used in various places for parameters.
 */
message Parameter {
  required string key = 1;
  required string value = 2;
}


/**
 * Collection of Parameter.
 */
message Parameters {
  repeated Parameter parameter = 1;
}


/**
 * Credential used in various places for authentication and
 * authorization.
 *
 * NOTE: A 'principal' is different from 'FrameworkInfo.user'. The
 * former is used for authentication and authorization while the
 * latter is used to determine the default user under which the
 * framework's executors/tasks are run.
 */
message Credential {
  required string principal = 1;
  optional bytes secret = 2;
}


/**
 * Credentials used for framework authentication, HTTP authentication
 * (where the common 'username' and 'password' are captured as
 * 'principal' and 'secret' respectively), etc.
 */
message Credentials {
  repeated Credential credentials = 1;
}


/**
 * ACLs used for authorization.
 */
message ACL {

  // Entity is used to describe a subject(s) or an object(s) of an ACL.
  // NOTE:
  // To allow everyone access to an Entity set its type to 'ANY'.
  // To deny access to an Entity set its type to 'NONE'.
  message Entity {
    enum Type {
      SOME = 0;
      ANY = 1;
      NONE = 2;
    }
    optional Type type = 1 [default = SOME];
    repeated string values = 2; // Ignored for ANY/NONE.
  }

  // ACLs.
  message RegisterFramework {
    // Subjects.
    required Entity principals = 1; // Framework principals.

    // Objects.
    required Entity roles = 2; // Roles for resource offers.
  }

  message RunTask {
    // Subjects.
    required Entity principals = 1; // Framework principals.

    // Objects.
    required Entity users = 2; // Users to run the tasks/executors as.
  }

  // Which principals are authorized to shutdown frameworks of other
  // principals.
  message ShutdownFramework {
    // Subjects.
    required Entity principals = 1;

    // Objects.
    required Entity framework_principals = 2;
  }
}


/**
 * Collection of ACL.
 *
 * Each authorization request is evaluated against the ACLs in the order
 * they are defined.
 *
 * For simplicity, the ACLs for a given action are not aggregated even
 * when they have the same subjects or objects. The first ACL that
 * matches the request determines whether that request should be
 * permitted or not. An ACL matches iff both the subjects
 * (e.g., clients, principals) and the objects (e.g., urls, users,
 * roles) of the ACL match the request.
 *
 * If none of the ACLs match the request, the 'permissive' field
 * determines whether the request should be permitted or not.
 *
 * TODO(vinod): Do aggregation of ACLs when possible.
 *
 */
message ACLs {
  optional bool permissive = 1 [default = true];
  repeated ACL.RegisterFramework register_frameworks = 2;
  repeated ACL.RunTask run_tasks = 3;
  repeated ACL.ShutdownFramework shutdown_frameworks = 4;
}


/**
 * Rate (queries per second, QPS) limit for messages from a framework to master.
 * Strictly speaking they are the combined rate from all frameworks of the same
 * principal.
 */
message RateLimit {
  // Leaving QPS unset gives it unlimited rate (i.e., not throttled),
  // which also implies unlimited capacity.
  optional double qps = 1;

  // Principal of framework(s) to be throttled. Should match
  // FrameworkInfo.princpal and Credential.principal (if using authentication).
  required string principal = 2;

  // Max number of outstanding messages from frameworks of this principal
  // allowed by master before the next message is dropped and an error is sent
  // back to the sender. Messages received before the capacity is reached are
  // still going to be processed after the error is sent.
  // If unspecified, this principal is assigned unlimited capacity.
  // NOTE: This value is ignored if 'qps' is not set.
  optional uint64 capacity = 3;
}


/**
 * Collection of RateLimit.
 * Frameworks without rate limits defined here are not throttled unless
 * 'aggregate_default_qps' is specified.
 */
message RateLimits {
  // Items should have unique principals.
  repeated RateLimit limits = 1;

  // All the frameworks not specified in 'limits' get this default rate.
  // This rate is an aggregate rate for all of them, i.e., their combined
  // traffic is throttled together at this rate.
  optional double aggregate_default_qps = 2;

  // All the frameworks not specified in 'limits' get this default capacity.
  // This is an aggregate value similar to 'aggregate_default_qps'.
  optional uint64 aggregate_default_capacity = 3;
}


/**
 * Describes a volume mapping either from host to container or vice
 * versa. Both paths can either refer to a directory or a file.
 */
message Volume {
  // Absolute path pointing to a directory or file in the container.
  required string container_path = 1;

  // Absolute path pointing to a directory or file on the host.
  optional string host_path = 2;

  enum Mode {
    RW = 1; // read-write.
    RO = 2; // read-only.
  }

  required Mode mode = 3;
}


/**
 * Describes a container configuration and allows extensible
 * configurations for different container implementation.
 */
message ContainerInfo {
  // All container implementation types.
  enum Type {
    DOCKER = 1;
  }

  message DockerInfo {
    // The docker image that is going to be passed to the registry.
    required string image = 1;
  }

  required Type type = 1;
  repeated Volume volumes = 2;

  optional DockerInfo docker = 3;
}