Framework-Agnostic Discovery

Tim Gross | Product Manager, Joyent | @0x74696d

Container-native?

Containers are a first class citizen.

Each container is an equal peer on the network.

Discovery should be framework-agnostic.

Remember: your mission is not "manage VMs."

Your mission is what your application does for your organization.

Infrastructure (undifferentiated heavy lifting) is incidental cost and incidental complexity.

Application containers make the full promise of cloud computing possible...

but require new ways of working.

Director of DevOps

... Docker in production since Oct 2013

What Docker Solved For Us:

Human-and-machine-readable build documentation.

No more "works on my machine."

Fix dependency isolation.

Interface-based approach to application deployment.

Deployments are fast!

DevOps kool-aid for everyone!

Ok, what's wrong?

Can we avoid NAT?

Can we avoid NAT?

DNS

Simple discovery! But...

Can't address individual hosts behind a record.*

No health checking.*

TTL caching.

Networking still sucks!

Containers don't have their own NIC on the data center network

Pass through proxy for all outbound requests

All packets go through NAT or port forwarding

The Container-Native Alternative?

Cut the cruft!

Push responsibility of the application topology away from the network infrastructure and into the application itself where it belongs.

Responsibilities of a Container

Registration

Self-introspection

Heartbeats

Look for change

Respond to change

No sidecars

Application-Aware Health Checks

No packaging tooling into another service

App container lifecycle separate from discovery service

Respond quickly to changes

Legacy Pre-Container Apps

• Registration: wrap start of app in a shell script
• Self-introspection: self-test?
• Heartbeats: um...
• Look for change: ???
• Respond to change: profit?

Containerbuddy:

A shim to help make existing apps container-native

• Registration: registers to Consul on startup
• Self-introspection: execute user-defined health check
• Heartbeats: send health status w/ TTL to Consul
• Look for change: poll Consul for changes
• Respond to change: execute user-defined response behavior

No Supervision

Containerbuddy is PID1

Returns exit code of shimmed process back to Docker Engine (or Triton) and dies

Attaches stdout/stderr from app to stdout/stderr of container

{
  "consul": "consul:8500",
  "services": [
    {
      "name": "nginx",
      "port": 80,
      "health": "/usr/bin/curl --fail -s http://localhost/health",
      "poll": 10,
      "ttl": 25
    }
  ],
  "backends": [
    {
      "name": "app",
      "poll": 7,
      "onChange": "/opt/containerbuddy/reload-nginx.sh"
    }
  ]
}
  

$ cat ./nginx/opt/containerbuddy/reload-nginx.sh

# fetch latest virtualhost template from Consul k/v
curl -s --fail consul:8500/v1/kv/nginx/template?raw \
    > /tmp/virtualhost.ctmpl

# render virtualhost template using values from Consul and reload Nginx
consul-template \
  -once \
  -consul consul:8500 \
  -template \
  "/tmp/virtualhost.ctmpl:/etc/nginx/conf.d/default.conf:nginx -s reload"
  

nginx:
  image: 0x74696d/containerbuddy-demo-nginx
  mem_limit: 512m
  ports:
  - 80
  links:
  - consul:consul
  restart: always
  environment:
  - CONTAINERBUDDY=file:///opt/containerbuddy/nginx.json
  command: >
    /opt/containerbuddy/containerbuddy
    nginx -g "daemon off;"
  

echo 'Starting Consul.'
docker-compose -p example up -d consul

# get network info from consul. alternately we can push this into
# a DNS A-record to bootstrap the cluster
CONSUL_IP=$(docker inspect example_consul_1 \
            | json -a NetworkSettings.IPAddress)

echo "Writing template values to Consul at ${CONSUL_IP}"
curl --fail -s -X PUT --data-binary @./nginx/default.ctmpl \
      http://${CONSUL_IP}:8500/v1/kv/nginx/template

echo 'Opening consul console'
open http://${CONSUL_IP}:8500/ui
  

Starting application servers and Nginx
example_consul_1 is up-to-date
Creating example_nginx_1...
Creating example_app_1...
Waiting for Nginx at 72.2.115.34:80 to pick up initial configuration.
...................
Opening web page... the page will reload every 5 seconds with any updates.
Try scaling up the app!
docker-compose -p example scale app=3
    

echo 'Starting application servers and Nginx'
docker-compose -p example up -d

# get network info from Nginx and poll it for liveness
NGINX_IP=$(docker inspect example_nginx_1 \
           | json -a NetworkSettings.IPAddress)
echo "Waiting for Nginx at ${NGINX_IP} to pick up initial configuration."
while :
  do
  sleep 1
  curl -s --fail -o /dev/null "http://${NGINX_IP}/app/" && break
  echo -ne .
done
echo
echo 'Opening web page... the page will reload every 5 seconds'
echo 'with any updates.'
open http://${NGINX_IP}/app/
  

Does it blend scale?

$ docker-compose -p example scale app=3
Creating and starting 2... done
Creating and starting 3... done