Bryan Cantrill on Docker's Remote API
Learn about Docker's true killer feature: the Docker Remote API. What exactly is it doing for developers, and what are the biggest issues facing developers?
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On May 6th, Bryan Cantrill spoke at a Docker/Joyent meetup in San Francisco, and elaborated on what he believes to be Docker's true killer feature: the Docker Remote API. He begins his talk with a pitch on Docker—on what exactly it's doing for developers and how. He also talks about how the biggest issue facing Docker is its use in production deployment. The main problems with Docker segue into a discussion of the Docker Remote API, what problems it solves, and how it can be used with other solutions.
1. Docker’s Killer Feature: The Remote API CTO firstname.lastname@example.org Bryan Cantrill @bcantrill
2. Docker revolution • Docker has used the rapid provisioning + shared underlying ﬁlesystem of containers to allow developers to think operationally • Developers can encode dependencies and deployment practices into an image • Images can be layered, allowing for swift development • Images can be quickly deployed — and re-deployed • Docker will do to apt what apt did to tar
3. Containers in production? • Docker’s challenges are largely around production deployment: security, network virtualization, persistence • Joyent runs OS containers in the cloud via SmartOS (our illumos derivative) — and we have run containers in multi-tenant production since ~2006 • Core SmartOS facilities are container-aware and optimized: Zones, ZFS, DTrace, Crossbow, SMF, etc. • SmartOS containers are designed for production: line- rate network virtualization, multi-tenant security, production debuggability, etc. • Could we somehow deploy Docker containers as SmartOS zones?
4. Docker + SmartOS: Linux binaries? • First (obvious) problem: while it has been designed to be cross-platform, Docker is Linux-centric • While Docker could be ported, the encyclopedia of Docker images will likely forever remain Linux binaries • SmartOS is Unix — but it isn’t Linux… • Fortunately, Linux itself is really “just” the kernel — which only has one interface: the system call table • We resurrected (and ﬁnished) a Sun technology for Linux system call emulation, LX-branded zones • Technical details of our Linux emulation are beyond the scope of this presentation...
5. LX-branded zones: tl;dr
6. LX-branded zones: tl;dr, cont.
7. Docker + SmartOS: Provisioning? • With the binary problem tackled, focus turned to the mechanics of integrating Docker with the SmartOS facilities for provisioning • Provisioning a SmartOS zone operates via the global zone that represents the control plane of the machine • docker is a single binary that functions as both client and server — and with too much surface area to run in the global zone, especially for a public cloud • docker has also embedded Go- and Linux-isms that we did not want in the global zone; we needed to ﬁnd a different approach...
8. Aside: The power of an interface
9. Aside: The power of an interface
10. Aside: The power of an interface
11. Aside: The power of an interface
12. Docker Remote API • While docker is a single binary that can run on the client or the server, it does not run in both at once… • docker (the client) communicates with docker (the server) via the Docker Remote API • The Docker Remote API is expressive, modern and robust (i.e. versioned), allowing for docker to communicate with Docker backends that aren’t docker • The clear approach was therefore to implement a Docker Remote API endpoint for SmartDataCenter
13. Aside: SmartDataCenter • Orchestration software for SmartOS-based clouds • Unlike other cloud stacks, not designed to run arbitrary hypervisors, sell legacy hardware or get 160 companies to agree on something • SmartDataCenter is designed to leverage the SmartOS differentiators: ZFS, DTrace and (esp.) zones • Runs both the Joyent Public Cloud and business-critical on-premises clouds at well-known brands • Born proprietary — but made entirely open source on November 6, 2014: http://github.com/joyent/sdc
14. SmartDataCenter: Architecture Booter AMQP broker Public API Customer portal ZFS-based multi-tenant ﬁlesystem VirtualNIC VirtualNIC Virtual SmartOS (OS virt.) ... VirtualNIC VirtualNICLinux Guest (HW virt.) ... VirtualNIC VirtualNIC Windows Guest (HW virt.) ... VirtualNIC VirtualNIC Virtual OS or Machine ... SmartOS kernel (network booted) SmartOS kernel (ﬂash booted) Provisioner Instrumenter Heartbeater DHCP/TFTP AMQP AMQP agents Public HTTP Head-node Compute node Tens/hundreds per head-node . . . SDC 7 core services BinderDNS Operator portal . . . Firewall
15. SmartDataCenter: Core Services Analytics aggregator Key/Value Service (Moray) Firewall API (FWAPI) Virtual Machine API (VMAPI) Directory Service (UFDS) Designation API (DAPI) Workﬂow API Network API (NAPI) Compute- Node API (CNAPI) Image API Alerts & Monitoring (Amon) Packaging API (PAPI) Service API (SAPI) DHCP/ TFTP AMQP DNS Booter AMQP broker Binder Public API Customer portal Public HTTP Operator portal Operator Services Manta Other DCs Note: Service interdependencies not shown for readability Head-node Other core services may be provisioned on compute nodes SDC7 Core Services
16. Docker Remote API for SmartDataCenter • Implementing an SDC-wide endpoint for the Docker remote API allows us to build in terms of our established core services: UFDS, CNAPI, VMAPI, Image API, etc. • Has the welcome side-effect of virtualizing the notion of Docker host machine: Docker containers can be placed anywhere within the data center • From a developer perspective, one less thing to manage • From an operations perspective, allows for a ﬂexible layer of management and control: Docker API endpoints become a potential administrative nexus • As such, virtualizing the Docker host is somewhat analogous to the way ZFS virtualized the ﬁlesystem...
17. Docker Remote API: Challenges • Some Docker constructs have (implicitly) encoded co- locality of Docker containers on a physical machine • Some of these constructs (e.g., --volumes-from) we discourage but accommodate by co-scheduling • Others (e.g., host directory-based volumes) we have implemented via Manta, our (open source!) distributed object storage service • Moving forward, we are working with Docker to help assure that the Docker Remote API doesn’t create new implicit dependencies on physical locality
18. Docker Remote API: Networking • Networking is an open area with respect to Docker • We have taken a VXLAN-/kernel-based (and ARP- inspired) approach to minimize latency, deliver line bandwidth and operate at scale • Our approach has the side effect of giving every container a full, isolated, virtualized IP stack • We use our in-kernel ﬁrewall support to impose the limitations implied by Docker’s • We are working with Docker to get the Remote API to be ﬂexible enough to accommodate constructs like ours
19. Joyent Triton: SmartOS + SDC + Docker • Our Docker engine for SDC, sdc-docker, implements the end points for the Docker Remote API • It’s open source: http://github.com/joyent/sdc-docker; you can install SDC (either on hardware or on VMware) and check it out for yourself! • We are explicit about our divergences from Docker: https://github.com/joyent/sdc-docker/blob/master/docs/divergence.md • We have stood this up in early access production under the Joyent Triton banner • A demo is worth a thousand slides...
20. The Remote API: Docker’s killer feature • Triton’s radically different approach is a vivid demonstration of the power of the Docker Remote API • Triton’s early adopters have been particular interested in the virtualization of the Docker host made possible by the Docker Remote API • It’s important that the Docker Remote API not imply physical co-locality — and be ﬂexible enough to accommodate radically different implementations • It’s critically important that upstack software not depend on the physical co-locality of Docker containers • By unlocking down-stack innovation, we believe Docker’s Remote API to be its killer feature!
21. Thank you! • @joshwilsdon, @trentmick, @cachaﬂa, @orlandov and Todd Whiteman for their work on sdc-docker • Jerry Jelinek, @pfmooney, @jmclulow and @jperkin for their work on LX branded zones • @rmustacc, @wayfaringrob, @fredfkuo and @notmatt for their work on SDC overlay networking • The countless engineers who have worked on or with illumos because they believed in OS-based virtualization
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