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dill

Cloud ready L4 TCP proxy with first-class support for dynamic listeners.

Exposing dynamic backends on the static frontend ports is the bread-and-butter of any modern proxy. Load balancing multiple dynamic backends from one ingress point using on-demand opened ports is something that, for a good reason as it might poise certain security concerns, is not that simple. But when you exactly know what you are doing you are pretty much on your own.

Table of Contents

Installation

Pre-build binaries

You can find pre-built binaries in Releases.

Build from sources

$ make build

Compiled binary will be available inside dist/ directory.

Docker

$ docker pull fwkz/dill

or build the image yourself from the sources

make image

Getting Started

First of all you have to define how you want to route the incoming traffic. dill provides multiple routing providers that allow you to apply live changes to the routing configuration. By far simplest approach is routing.file.

# /etc/dill/config.toml
[routing.file]
  path = "/etc/dill/routing.toml"
  watch = true 
# /etc/dill/routing.toml
[[services]]
  name = "foo"
  listener = "any:1234"
  backends = ["192.168.10.1:5050"]
$ dill -config /etc/dill/config.toml

And that's it! dill will accept the traffic on 0.0.0.0:1234 and load balance it between services running on 192.168.10.1:5050 and 192.168.10.2:4050. Make sure to read more about interface labels, e.g., any, local

Now imagine that you spawned another service that accepts traffic on port 4444 and you'd like to expose it on running dill instance without any downtime to already load balanced services. It's dead simple, you just add a new entry:

# /etc/dill/routing.toml
[[services]]
  name = "foobar"
  listener = "any:1234"
  backends = ["192.168.10.1:5050, 192.168.10.2:4050"]

[[services]]
  name = "bar"
  listener = "any:4321"
  backends = ["192.168.10.3:4444"]

dill will automatically pick up the changes and apply necessary modifications to its routing table. Service bar is now available on the host running the dill on port 4321.

If you are using a modern workload scheduler like Nomad or Kubernetes this idea becomes very powerful. For instance, using Consul routing provider with just a few tags you can expose dynamically spawned backends with no proxy downtime.

Routing

Providers

dill offers multiple routing providers that allow you to apply live changes to the routing configuration.

You can help build the project and implement your routing provider based on your needs. If you need guidance, make sure to create Pull Request.

File

It is the simplest way of defining routing. All routing logic is being kept in a separate config file. By setting routing.file.watch = true you can also subscribe to changes made to the routing configuration file which would give you the full power of dill's dynamic routing capabilities.

[routing.file]
  path = "/etc/dill/routing.toml"
  watch = true

HTTP

dill can poll the HTTP endpoint for its routing configuration with a predefined time interval. Fetched data should be compliant with routing configuration schema and it will be parsed based on the response Content-Type header.

[routing.http]
  endpoint = "http://127.0.0.1:8000/config/routing.json"
  poll_interval = "5s"
  poll_timeout = "5s"

Consul

dill can build its routing table based on services registered in Consul. All you need to do in order to expose Consul registered service in dill instace is to add appropriate tags.

  • dill tag registers service and its updates with dill instance.
  • dill.listener binds, based on predefined listeners declared by listeners.allowed, service to specific address and port.
{
  "service": {
    "tags": [
      "dill",
      "dill.listener=local:5555",
    ],
  }
}

In order to pass traffic via proxy make sure to add dill.proxy tag:

{
  "service": {
    "tags": [
      "dill",
      "dill.listener=local:5555",
      "dill.proxy=socks5://admin:[email protected]:1080"
    ],
  }
}

Example configuration of Consul routing provider:

[routing.consul]
  address = "http://127.0.0.1:8500"
  token = "consul-communication-secret-token"
  datacenter = "foo-1"  
  namespace = "bar-namespace"
  wait = "2m"
  consistency_mode = "consistent"

Nomad

Since version 1.3.0 Nomad introduced native service discovery. Principales of exposing Nomad workloads in dill are exactly the same as for Consul routing provider.

Example service block of Nomad job.

service {
  name     = "foobar"
  tags     = ["dill", "dill.listener=any:3821"]
  port     = "db"
  provider = "nomad"

  check {
    name     = "alive"
    type     = "tcp"
    interval = "10s"
    timeout  = "2s"
  }
}

Example configuration of Nomad routing provider:

[routing.nomad]
  address = "http://127.0.0.1:4646"
  token = "nomad-communication-secret-token"
  namespace = "foobar-namespace"
  wait = "5m"
  stale = true
[routing.nomad.tls]
  ca = "/foo/bar/ca"
  cert = "/foo/bar/cert"
  key = "/foo/bar/key"
  insecure = false

Load balancing

dill distributes load across the backends using round-robin strategy

Schema

The routing configuration should be compliant with following schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "services": {
      "type": "array",
      "items":{
        "type": "object",
        "properties": {
          "name": {"type": "string"},
          "listener": {"type": "string"},
          "backends": {"type": "array", "items": {"type": "string"}},
          "proxy": {"type": "string"}
        },
        "required": [
          "name",
          "listener",
          "backends"
        ]
      }
    }
  },
  "required": [
    "services"
  ]
}

Example routing config:

{
  "services": [
    {
      "name": "foo",
      "listener": "local:1234",
      "backends": [
        "127.0.0.1:5050"
      ],
      "proxy": "socks5://user:[email protected]:1080"
    },
    {
      "name": "bar",
      "listener": "any:4444",
      "backends": [
        "127.0.0.1:4000",
        "127.0.0.1:4001"
      ]
    }
  ]
}

or equivalent in different format e.g. TOML, YAML:

# /etc/dill/routing.toml
[[services]]
  name = "foo"
  listener = "local:1234"
  backends = ["127.0.0.1:5050"]
  proxy = "socks5://user:[email protected]:1080"  # optional

[[services]]
  name = "bar"
  listener = "any:4444"
  backends = ["127.0.0.1:4000", "127.0.0.1:4001"]
services:
  - name: foo
    listener: local:1234
    backends:
      - 127.0.0.1:5050
    proxy: socks5://user:[email protected]:1080
  - name: bar
    listener: any:4444
    backends:
      - 127.0.0.1:4000
      - 127.0.0.1:4001

name

Name of the service.

listener

Listener that binds, based on predefined list declared by listeners.allowed, backend to specific address and port.

backends

List of backend services that will be load balanced.

proxy

Proxy address if you want to tunnel the traffic.

Optional

Proxying

dill is capable of tunneling traffic to backend services using SOCKS proxy.

# /etc/dill/routing.toml
[[services]]
  name = "foobar"
  listener = "any:4444"
  backends = ["192.168.10.11:4001"]
  proxy = "socks5://user:[email protected]:1080"
     incoming      ┌───────────┐        ┌─────────────┐         ┌───────────────┐
─────connection────►4444  dill ├────────►1080  SOCKS  ├─────────►4001  Backend  │
                   └───────────┘        └─────────────┘         └───────────────┘
                                         192.168.10.10            192.168.10.11

Configuration

dill already comes with sane defaults but you can adjust its behaviour providing configuration file

$ dill -config config.toml

or use environment variables

$ export DILL_CONSUL_ADDRESS="http://127.0.0.1:8500"
$ DILL_LISTENERS_PORT_MIN=1234 dill

Values

listeners.allowed map

Interface addresses that are allowed to be bind to by upstream services. Address labels (keys in the map) are opaque for dill.

Imagine that a machine hosting dill has two interfaces, one is internal (192.168.10.10) and the other is external (12.42.22.65). You might want to use the following setup

[listeners.allowed]
internal = "192.168.10.10"
public = "12.42.22.65"

with such configuration, upstream services that want to be accessible on 12.42.22.65:5555 can use the public listener in Consul tags dill.listener=public:5555.

default: {"local": "127.0.0.1", "any": "0.0.0.0"}

listeners.port_min integer

Minimal port value at which it will be allowed to expose upstream services. Backends requesting to be exposed on lower ports will be dropped from routing.

default: 1024

listeners.port_max integer

Maximum port value at which it will be allowed to expose upstream services. Backends requesting to be exposed on higher ports will be dropped from routing.

default: 49151

peek.listener string

Address on which Peek will be exposed. Peek is a TCP debug server spawned alongside the dill. Connecting to it will return the current state of the routing table. By default Peek is turned off.

default: ""

$ nc 127.0.0.1 2323
0.0.0.0:4444
  ├ round_robin
  ├──➤ 192.168.10.17:1234
  ├──➤ 192.168.10.23:2042
0.0.0.0:8088
  ├ round_robin
  ├──➤ 192.168.10.11:5728
  ├──➤ 192.168.65.87:5942

runtime.gomaxprocs integer

Value of Go's runtime.GOMAXPROCS()

default: equals to runtime.NumCPU()

routing.file.path string

Location of routing configuration file.

routing.file.watch bool

Subscribe to changes made to the routing configuration file which would give you the full power of dill's dynamic routing capabilities.

default: true

routing.http.endpoint string

Endpoint which http provider will poll for routing configuration

routing.http.poll_interval duration

How often http provider will poll endpoint for routing configuration

default: 5s

routing.http.poll_timeout duration

Maximum time http provider will wait when fetching routing configuration

default: 5s

routing.consul.address string

Consul address from which dill will fetch the updates and build the routing table.

routing.consul.token string

Token giving access to Consul API. Required ACLs node:read,service:read

Optional

routing.consul.datacenter string

Defines what datacenter will be queried when building routing table.

Optional. If not provided dill uses Consul defaults.

routing.consul.namespace string

Defines what namespace will be queried when building routing table. Namespaces are available only for Consul Enterprise users.

Optional. If not provided dill uses Consul defaults.

routing.consul.wait duration

Defines how long blocking API query will wait for a potential change using long polling.

Optional. If not provided dill uses Consul defaults.

routing.consul.consistency_mode string

Defines what consistency mode to use when dill fetches the updates.

Optional. Allowed values: stale, consistent, leader. If not provided dill uses Consul defaults.

routing.nomad.address string

Nomad address from which dill will fetch the updates and build its routing table.

routing.nomad.token string

Token giving access to Nomad API. Required ACLs namespace:read-job

Optional.

routing.nomad.namespace string

Defines what namespace will be queried when building routing table.

Optional. If not provided dill uses default Nomad namespace.

routing.nomad.wait duration

Defines how long blocking API query will wait for a potential change using long polling.

Optional. If not provided dill uses Nomad defaults.

routing.nomad.stale bool

stale allows any Nomad server (non-leader) to service a read. This allows for lower latency and higher throughput. This means reads can be arbitrarily stale; however, results are generally consistent to within 50 milliseconds of the leader.

Optional. Default: false

routing.nomad.tls.ca string

Path to a PEM-encoded CA cert file to use to verify the Nomad server SSL certificate.

Optional. Defaults to the system bundle.

routing.nomad.tls.cert string

Path to the certificate used for secure communication with Nomad.

Optional.

routing.nomad.tls.key string

Path to the key used for secure communication with Nomad. It's required if routing.nomad.tls.cert is used.

Optional.

routing.nomad.tls.insecure bool

Disables certificate verification.

Optional. Default: false

Formats

Configuration is powered by Viper so it's possible to use format that suits you best.

reading from JSON, TOML, YAML, HCL, envfile and Java properties config files

dill uses the following precedence order:

  • environment variable
  • config file
  • default value

TOML

[listeners]
port_min = 1024
port_max = 49151

[listeners.allowed]
local = "127.0.0.1"
any = "0.0.0.0"

[routing.consul]
address = "http://127.0.0.1:8500"

[peek]
listener = "127.0.0.1:4141"

[runtime]
gomaxprocs = 4

YAML

listeners:
  port_min: 1024 
  port_max: 49151
  allowed:
    local: "127.0.0.1"
    any: "0.0.0.0"

routing:
  http:
    endpoint: "http://127.0.0.1:8000/config/routing.json"
    poll_interval: "5s"
    poll_timeout: "5s"

peek:
  listener: "127.0.0.1:4141"

runtime:
  gomaxprocs: 4

JSON

{
  "listeners": {
    "port_min": 1024,
    "port_max": 49151,
    "allowed": {
      "local": "127.0.0.1",
      "any": "0.0.0.0"
    }
  },
  "routing": {
    "file": {
      "path": "/Users/fwkz/Devel/dill/configs/routing.toml",
      "watch": true
    }
  },
  "peek": {
    "listener": "127.0.0.1:4141"
  },
  "runtime": {
    "gomaxprocs": 4
  }
}

Environment variables

Variables should be prefixed with DILL and delimited with underscore e.g. consul.address becomes DILL_CONSUL_ADDRESS.

$ export DILL_CONSUL_ADDRESS="http://127.0.0.1:8500"
$ DILL_LISTENERS_PORT_MIN=1234 dill

Project status

Concept of dynamic listeners is experimental and should be used with responsibility. There might be some breaking changes in the future.

Alternatives