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139 lines
5.2 KiB
Markdown
139 lines
5.2 KiB
Markdown
## Unikernel System Containers
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### General Architecture
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```
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|=================| |================|
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| privileged shim | | calf |
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|=================| |================|
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| | | |
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<-- eth0 ---> | eBPF rules | <--- network IO ---> | type-safe |
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| | (data path) | network stack |
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| | | |
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|-----------------| |----------------|
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<-- logs ----- | | <------- logs ------ | type-safe |
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| | | protocol logic |
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<-- metrics -- | | <----- metrics ----- | |
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|-----------------| |----------------|
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<-- audit --- | config store | <----- KV store ---> | config store |
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diagnostic | deamon | (control path) | client |
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|_________________| |________________|
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<-- sycalls -- | |
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| system handlers |
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<-- config --- | |
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files | |
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|_________________|
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```
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1. privileged shim (privileged system service)
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- run in a privileged container
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- can read all network traffic
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- can set-up eBPF rules (or a dumb forwarder to start with)
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- exposes an easily auditable KV store for configuration values
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(over a simple REST/HTTP API to start with).
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Expose a scoped "view" of the config store to the
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calf (a different branch in a datakit store for instance) and another
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unscoped "view" to the host (could be a Git log if using datakit).
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- has a set of system handlers who watches for changes in the KV
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store and perform privileged operations inside moby (syscalls, edit
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global config files, etc). System handlers use the config store CLI
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to wait for events and react.
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2. calf (sandboxed system service)
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- run in a fully isolated container
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- full sandbox (initially a normal Unix process, later on unielf/wasm)
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- has a type-safe network stack to handle network IO
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- has type-safe business logic to process network IO
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- has a limited access read and write access to the config store where the
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result of the business logic is output
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### DHCP client
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#### Shim
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- forward DHCP traffic only (in both directions)
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- expose a simple store to the calf, with the following keys:
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```
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/ip (mandatory)
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/mtu (optional)
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/domain (optional)
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/search (optional)
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/nameserver/001 (optional)
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...
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/nameserver/xxx (optional)
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```
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If runs a small webserver where it exposes a simple CRUD interface
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over these keys -- only the calf can see it (e.g. it opens a pipe and
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share it with the calf on startup).
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- system handlers:
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- if /ip change -> set IP address on moby host
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- if /domain change -> set moby domain name
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- if /search -> set search domain on moby host
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- if /nameserver/xxx -> set DNS servers on moby
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#### Calf
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- MirageOS unikernel using charrua-client (or a fork of it).
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- Has access to a Mirage_net.S interface for network traffic
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- Has access to a a simple KV interface
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Internally, it uses something more typed than a KV store:
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```
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module Shim: sig
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val set_ip: Ipaddr.V4.t -> unit Lwt.t
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val set_domain: string -> unit Lwt.t
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val set_search: string -> unit Lwt.t
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val set_nameservers: Ipaddr.V4.t list Lwt.t
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end
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```
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but this ends up being translated into REST/RPC calls to the shim.
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### SDK
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What the SDK should enable:
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1. easily write a new calfs initially in OCaml, then Rust.
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Probably not very useful on its own.
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2. easily write a new shim by providing the basic blocks:
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eBPF scripts, calf runner, KV store, system handlers.
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Initially could be a standalone blob, but should aim for
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independant and re-usable pieces that could run in a
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container.
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3. (later) generate shim/caft containers from a single (API?)
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description.
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### Roadmap
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#### first PoC: DHCP client
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Current status: one container containing two static binaries (priv + calf),
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private pipes open between the process for stdout/stderr aggregation +
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raw sockets (data path). Control path is using a simple HTTP server running
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in the priv container. The calf is using the dev version of mirage/charrua-core,
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and is able to get a DHCP lease on boot.
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##### TODO
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- use runc to isolate the calf
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- system handler (see https://github.com/kobolabs/dhcpcd/tree/kobo/dhcpcd-hooks)
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- use seccomp to isolate the privileged container
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- use the DHCP results to actually update the system
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- add metrics aggregation (using prometheus)
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- better logging aggregation (using syslog)
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- IPv6 support
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- tests, tests, tests (especially against non compliant RFC servers)
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### Second iteration: NTP
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TODO
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