Mesos笔记 （9）—— Containerizer类代码解析

Containerizer类（定义在src/slave/containerizer/containerizer.hpp ）是所有Containerizer的抽象父类。除了默认的构造函数和一个什么都没做的析构函数，其只实现了create和resources方法。create方法代码如下（v0.26版本）：

Try<Containerizer*> Containerizer::create(
    const Flags& flags,
    bool local,
    Fetcher* fetcher)
{
  if (flags.isolation == "external") {
    LOG(WARNING) << "The 'external' isolation flag is deprecated, "
                 << "please update your flags to"
                 << " '--containerizers=external'.";

    Try<ExternalContainerizer*> containerizer =
      ExternalContainerizer::create(flags);
    if (containerizer.isError()) {
      return Error("Could not create ExternalContainerizer: " +
                   containerizer.error());
    }

    return containerizer.get();
  }

  // TODO(benh): We need to store which containerizer or
  // containerizers were being used. See MESOS-1663.

  // Create containerizer(s).
  vector<Containerizer*> containerizers;

  foreach (const string& type, strings::split(flags.containerizers, ",")) {
    if (type == "mesos") {
      Try<MesosContainerizer*> containerizer =
        MesosContainerizer::create(flags, local, fetcher);
      if (containerizer.isError()) {
        return Error("Could not create MesosContainerizer: " +
                     containerizer.error());
      } else {
        containerizers.push_back(containerizer.get());
      }
    } else if (type == "docker") {
      Try<DockerContainerizer*> containerizer =
        DockerContainerizer::create(flags, fetcher);
      if (containerizer.isError()) {
        return Error("Could not create DockerContainerizer: " +
                     containerizer.error());
      } else {
        containerizers.push_back(containerizer.get());
      }
    } else if (type == "external") {
      Try<ExternalContainerizer*> containerizer =
        ExternalContainerizer::create(flags);
      if (containerizer.isError()) {
        return Error("Could not create ExternalContainerizer: " +
                     containerizer.error());
      } else {
        containerizers.push_back(containerizer.get());
      }
    } else {
      return Error("Unknown or unsupported containerizer: " + type);
    }
  }

  if (containerizers.size() == 1) {
    return containerizers.front();
  }

  Try<ComposingContainerizer*> containerizer =
    ComposingContainerizer::create(containerizers);

  if (containerizer.isError()) {
    return Error(containerizer.error());
  }

  return containerizer.get();
}

默认情况下，containerizers的type是mesos，所以会调用MesosContainerizer::create来生成containerizer。关于resources方法，参考Mesos笔记 （5）—— 资源。