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  1. 1. Clustering Unikernel Microservices in Networking Myungho Jung University of Utah I. INTRODUCTION As the scale of web services is growing, Microser- vices architecture is becoming a trend to develop large-scale web applications. Web services consists of a lot of more scalable, less coupling small appli- cations that can be combined into a large system. As the Microservices becomes popular, the compat- ibility between platforms is one of the crucial fac- tors in deciding the quality of the application. There are several ways to deploy applications as Microser- vices. First, an application itself can be deployed on a host. Although it is straightforward and efficient when it comes to dealing with resources, it is not optimal when it comes to portability. In other words, it would not work if the platform or operating system of host is different from developed environment. One of the solution is using container like Docker. Container consists of required libraries and applica- tions. The advantage of the container is fast and com- patible on the same sort of kernel. However, it shares the kernel with guest OS which would be vulnerable to attacks aiming host kernel. Running applications on virtual machine can also be a solution. The difference from the container is that each VM runs on separate kernel unlike the con- tainers sharing kernel. By doing so, it would be se- curer from kernel attacks at the cost of performance. Unikernel is a new approach that merges the advan- tages of container and virtual machine. It is basically based on the virtual machine but it is packaged with the only required frameworks and libraries. There- fore, it minimizes the attack surface by excluding un- necessary parts such as terminal input or ssh. Al- though this may make difficult to debug and test appli- cations, it will make safer than containers and other external tools will help the development. In this project, I focused on the clustering of uniker- nel Microservices. Although unikernel is secure and lightweight, defining networks for a bunch of uniker- nel application in a host is not an easy work. To sim- plify this, I suggested a way to abstract the internal networks of unikernels working closely. It converts multiple unikernel instances into a host in network layer. For deployment of the service to hosts, python script and a configuration file are necessary to repli- cate the Openflow[2] network. The flows not only de- fines which guest OS is accessible from outside, but also offers secure networking inside. II. MOTIVATION In a nutshell, the objective of the project is to ab- stract the internal networking structure and to make a group of unikernels look a host in the higher level of networking. Microservices using unikernel is secure and easy to deploy. However, it sometimes involves a lot of work to integrate or duplicate web applica- tions. Here’s an example of the real world problem. In FIG. 1. Example of integrating services FIG. 1, assume that web services that are developed in different company or host. The problem is that it requires to set up a new network structure and re- build virtual machine images including IP address in application code. Although it would be simple in this example, more complicated and long process would be involved as the number of applications in a host increases. FIG. 2. Pre-configured VM images for Web service Let’s start from simpler example. As seen in FIG. 2, three virtual machines, which are nginx, PHP, and MySQL servers, are running. It would make the prob- lem clear. Assume that an administrator of a host wants to run multiple services using the images. We
  2. 2. 2 can dynamically change the IP of each instance by set- ting option parameters. The problem is caused by the fixed IP addresses in web application code and server configuration file. In this case, nginx image includes the IP addresses of PHP and MySQL servers and we should rebuild the image to modify them. However, tt is not always necessary to modify the code. The FIG. 3 shows no need to rebuild images for serving multiple services. In this case, it is enough to change the IP of FIG. 3. A case of no IP confliction between services nginx servers to avoid IP confliction. However, it may not much secure because every user should share PHP and MySQL servers. Thus, each user would ask to create separate VMs from others. To avoid IP conflic- tion and run a virtual machine per user, Linux network namespace helps to accomplish it. The solution is cre- ating a network name space for each user and running instances inside of it in FIG. 4. Then, each virtual ma- chine that have the same IP can run on a host if layer 2 networking is carefully handled. In some cases, multi- FIG. 4. An example requiring network namespaces to avoid IP confliction ple Microservices are required to share resources and to work together. In FIG.5, the MySQL server would not be able to generate ARP table for each php server if the IP of two servers is the same. So, we need to allocate a virtual IP for each group of virtual instaces. By doing so, we don’t have to care about IP confliction, but also different subnet from that of virtual machines can be used in host OS. FIG. 5. Sharing a service from different hosts III. RELATED WORKS Unikernel is still in early stage compared to con- tainers and thus, there are few project on clustering unikernel. On the other hand, microservices on con- tainers are being used for production. There are many project related to clustering containers. One of the most popular projects is Kubernetes[7]. It defines a group of containers working together as a pod. It’s a large-scale project working on scaling, scheduling and orchestration of containers. In addition, Tectonic[5] is a project from CentOS for cluster management of containers. It supports docker and CentOS Rocker containers. Docker project is also working on Docker Swarm[6] to cluster containers using docker API. On top of the clustering, Apache Mesos[4] is dealing with scaling and automated deployment. Amazon EC2[9] is supporting the management and clustering of con- tainers on the cloud platform. Containers are required to replicated for scaling and load balancing. It is an important factor for Microservices. In spite of the popularity and maturity of containers, unikernel is emerging as a new platform for Microser- vices. Docker which is one of the most famous con- tainer already decided to support unikernel. Uniker- nel Microservices will make the system securer by iso- lating the kennel of instances from each other. IV. SECURITY A. Threat Model Unikernel is rather secure since it runs on sepa- rate kernel from others. Therefore, even if the ker- nel is compromised by an attacker, it is hard to at- tack the next virtual machine directly. Nevertheless, we still need to carefully deal with packet flow be- tween virtual machines. Instead of setting firewalls for each guest OS, we can utilize Openflow for allow-
  3. 3. 3 ing or block path between two hosts. In FIG. 6, PHP FIG. 6. Packet flows allowed and blocked server needs to access MySQL to retrieve data. How- ever, the nginx server doesn’t need to directly access the database. If the path is allowed, an attacker may be able to try SQL injection attack through the nginx server. One of the drawbacks for unikernel Microservice is that it is hard to run rootkit or virus vaccine be- cause virtual machines have limited amount of CPU and memory. In addition, if there are tens or hundreds of instances are running on a host, monitoring pack- ets on each host would cost a lot of resources. For- tunately, the booting time for unikernel is extremely short and thus, it would be better to reboot if the kernel is compromised or an attack is detected. To do this, Intrusion Detection System(IDS) connected to Software Defined Networks(SDN) controller would help to monitor packets from outside. When it detects a suspicious packets to a VM, we can choose an ac- tion to handle it such as, rebooting the VM, checking by rootkit tool, or rolling back data. V. IMPLEMENTATION Rump kernel[3], Openvswitch[1], Floodlight SDN controller[8], and python scripts are used for con- structing network. After booting rump kernels with openvswitch bridges, openflows are added for layer 2 and 3 networking. This process is automated by python script with json configuration file. A. Rump Kernels Rumpkernel is one of the unikernel project using NetBSD kernel. The advantage is that the kernel is rather stable and light. In general, the booting time is in seconds and thus, it is much faster than gen- eral VMs. In security, it may secure than containers like Docker because guest OS doesn’t share the ker- nel with Domain 0. One of the challenges in implementation is that some guest OS should have two IP addresses for in- ternal and external networking. In this project, I de- cided to add an additional network interface to avoid changing routing table in guest OS. In this case, two virtual machines may have the same external IP. Thus, flow rules in network layer 2 and 3 should be carefully managed. B. Open vSwitch Open vSwitch provides bridges for virtual ma- chines. It is working in layer 2 network, however, layer 3 network can also be controllable with Open- flow protocol[2]. In this project, there is a central bridge and it is connected to other bridges for each group of virtual machines. Even if the bridges are connected directly, we can generate any networking topology by managing Openflow. Bridges for each group of unikernels should be di- rectly connected the central bridge, which means ev- ery bridge can access each other without Openflow. However, thanks to the Openflow, we can create any network topology by defining flows between bridges. FIG. 7 shows possible topologies when 4 bridges are connected to a central bridge. FIG. 7. Examples of network topologies C. Floodlight Floodlight is a SDN controller that can push static flows on a bridge. It also helps to monitor traffic on network and manage flows. We can connect Intrusion
  4. 4. 4 Detection System to the controller in order to monitor packets and decide a host that should reboot if the kernel is compromised. D. Deployment it is difficult to manage flows on a lot of bridges, even if a SDN controller is used. To automate the pro- cess, a python script with a configuration file is devel- oped for this project. As a result, only necessary files for the deployment are virtual machines and a config- uration file. The deployment process is simple. First, create bridges for each group of virtual machines and con- nect time to the central bridge to make accessible. Af- ter that, add extra network interfaces using rumprun parameter to instances that should be access to oth- ers in different bridges. And modify the configuration file according to the settings on bridges. Finally, exe- cuting script with the configuration file. Listing 1. An example of json configuration file { "name": "wordpress-user1", "birdge": "br-wp-user1", "external-ip": "", "hosts": [ { "name": "nginx", "mac": "00:00:00:00:00:01", "ip": "", "tcp-port": "80", "bridge-port": "5" }, { "name": "php", "mac": "00:00:00:00:00:02", "ip": "", "tcp-port": "8000", "bridge-port": "6" }, { "name": "mysql", "mac": "00:00:00:00:00:03", "ip": "", "tcp-port": "3306", "bridge-port": "7" }, ], "internal-flows": [ { "from":"nginx", "to":"php" }, { "from":"php", "to":"mysql" } ], "external-ports": [ { "src-ip": "", "to": "" } ] } The python script parses the json file and push static flows to bridges. Even if this process will be enough to implement with Open vSwitch CLI, Floodlight REST API is used to maintain flows with name. [1] Open vswitch. Accessed: 2016-04-02. [2] Openflow. Accessed: 2016-04-02. [3] Rump kernels. Accessed: 2016-04-02. [4] Apache. Apache mesos. Accessed: 2016-04-02. [5] CentOS. Coreos tectonic. Ac- cessed: 2016-04-02. [6] Docker. Docker swarm. swarm/. Accessed: 2016-04-02. [7] Google. Kubernetes. Accessed: 2016-04-02. [8] A Big Switch Network. Project floodlight. http://www. Accessed: 2016-04-02. [9] Amazon Web Service. Amazon ec2 container service. Accessed: 2016-04-02.