Docker Architecture (v1.3)

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Docker Architecture (based on v 1.3)

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Docker Architecture (v1.3)

  1. 1. Docker Architecture based on v 1.3 Compiled by Rajdeep Dua Twi?er : @rajdeepdua Oct 2014 Tuesday, November 4, 14
  2. 2. Before we get started • What is a Container? – Group of processes contained in a Isolated Environment – IsolaNon provided by Concepts like cgroups and namespaces • What is Docker? – ImplementaNon of a container which is portable using a concept of image. Tuesday, November 4, 14
  3. 3. CGroup • Limit, account, and isolate resource usage (CPU, memory, disk I/O, etc.) of process groups. • Resource limi@ng: groups can be set to not exceed a set memory limit — this also includes file system cache. • Priori@za@on: some groups may get a larger share of CPU[8] or disk I/O throughput. • Accoun@ng: to measure how much resources certain systems use • Control: freezing groups or checkpoin@ng and restar@ng. Tuesday, November 4, 14
  4. 4. Namespace • ParNNon essenNal kernel structures to create virtual environments • Different Namespaces – pid (processes) – net (network interfaces, rouNng...) – ipc (System V IPC) – mnt (mount points, filesystems) – uts (hostname) – user (UIDs) Tuesday, November 4, 14
  5. 5. Docker • Manages Images and Container runNmes • Supports mulNple file system back-­‐ends • MulNple Execdrivers for container implementaNon • Client and server components – interacNon using HTTP using unix sockets Tuesday, November 4, 14
  6. 6. Docker RunNme Components Tuesday, November 4, 14
  7. 7. Docker Engine • Core of Docker : Store for Containers • Manages containers using Jobs (similar to Unix jobs) • Contains Handlers a funcNon which wraps Jobs • All the acNons performed using Jobs Engine n 1 1 1 Handler Job Tuesday, November 4, 14
  8. 8. Docker IniNalizaNon 1. Main funcNon of Docker : docker.main() 2. Calls : mainDaemon() 3. InstanNate Engine eng := engine.New() 4. Register built-­‐ins builtsin.Register(eng) 5. InstanNate job job := eng.Job(“initserver”) 6. Set Env variables for the Job Tuesday, November 4, 14
  9. 9. Docker IniNalizaNon 5. Run the Job job.run() 6. Start AccepNng ConnecNons eng.Job(“AcceptConnections”).run() Tuesday, November 4, 14
  10. 10. Docker IniNalizaNon : 4 4. Register built-­‐ins Instantiate daemon(eng) //see later slides for details eng.Register("initserver", server.InitServer) //see later slides for details eng.Register(“init_networkdriver”, bridge.InitDriver) Tuesday, November 4, 14
  11. 11. Daemon • Main Entry point for all the requests to manage containers • Data Structure which maintains following references – ImageGraph – Volume Graph – Engine – ExecDriver – Server – ContainerStore Tuesday, November 4, 14
  12. 12. Daemon -­‐ Graph • Graph is a (structure) store of versioned file system and rela@onship between images • For each container a Graph is instan@ated • References a graphdriver.Driver • Ac@ons on a Graph – Create a New Graph – Get image from a Graph – Restores a Graph – Creates an Image and Register in the Graph – Registers a pre-­‐exis@ng image on the Graph Tuesday, November 4, 14
  13. 13. Concept of Images and Containers in Docker • Docker image is a Layer in the file System • Containers are two Layers – Layer one is init layer based on Image – Layer two is the actual container content Container Content Image Content Layer Init Layer Docker Container Tuesday, November 4, 14
  14. 14. Container in Docker • DataStructure which resides in-­‐memory and is persisted in SQLite store • References other components like – Daemon – Volumes – Has a lifecycle which is controlled by Daemon – Daemon has in-­‐memory dicNonary of containerIDs and containers 14 Tuesday, November 4, 14
  15. 15. Lifecycle of a Container 15 Tuesday, November 4, 14
  16. 16. Graph Driver • Referenced by the Daemon • Used to abstract mulNple storage backends • Loads one of the following File System Backends – aufs – Device mapper (devmapper) – vfs – btrfs Tuesday, November 4, 14
  17. 17. Container store • Persistent backend for Container data • Implemented using SQLite • Referenced from Daemon containerGraph: graph Used to load container informaNon during Daemon restore Tuesday, November 4, 14
  18. 18. Volume Graph • Simple vfs based Graph to keep track of container volumes • Volumes used volume driver in Daemon to create and a?ach volumes to the container • Each container is associated with one of more volumes Tuesday, November 4, 14
  19. 19. ExecDriver • AbstracNon for the underlying Linux Containment • Called from the daemon • Supports following implementaNon – LXC – NaNve Tuesday, November 4, 14
  20. 20. Driver Interfaces • Abstract Interface to interact with the underlying implementaNon. type driver Interface{ Run(c *Command,..) Kill(c *Command) Pause(c *Command) Name() GetProcessIdsForContainer(id string) Terminate() } Tuesday, November 4, 14
  21. 21. Driver Interfaces -­‐ Networking • Abstract Interface to interact with the underlying implementaNon. type Network struct { Interface *NetworkInterface Mtu int ContainerID string HostNetworking bool } Tuesday, November 4, 14
  22. 22. libcontainer • Underlying naNve implementaNon of the Container • Used by the naNve driver • Container.config – representaNon of a container data • Wrapper over cgroups and Namespaces Tuesday, November 4, 14
  23. 23. NaNve Driver ImplementaNon Tuesday, November 4, 14
  24. 24. Steps in Container CreaNon Container Create Tuesday, November 4, 14
  25. 25. Container Commit Tuesday, November 4, 14
  26. 26. Summary • Linux Containment Principles • Docker Architectural components • NaNve Driver ImplementaNon – libcontainer • ContainerCreaNon Tuesday, November 4, 14

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