fleet is no longer actively developed or maintained by CoreOS. CoreOS instead recommends Kubernetes for cluster orchestration.
The following is an example of how one might deploy a load-balanced web service using fleet. This example deploys subgun, a simple subscription tool for mailgun.
subgun is deployed in two pieces: an application and a presence daemon. The application simply serves HTTP requests through an AWS load balancer, while the presence daemon updates the load balancer with backend information. The diagram below illustrates this model:
Both components are deployed in docker containers running on CoreOS. The following Dockerfiles were each built and their resulting images pushed to the public docker index:
coreos/subgun
FROM stackbrew/ubuntu:precise
RUN apt-get install -y --allow-unauthenticated ca-certificates
ADD bin/subgun /bin/
EXPOSE 8080
ENV SUBGUN_LISTEN 127.0.0.1:8080
CMD /bin/subgun
quay.io/coreos/elb-presence
FROM ubuntu:14.04
RUN apt-get update
RUN apt-get install -y python-boto
ADD elb-presence /bin/elb-presence
CMD /bin/elb-presence
With the docker images available over the public internet, systemd can simply run the containers.
The following unit files are templates, which means they can be run multiple times by referencing them with full instance names. You can find these unit files in the unit-examples repository. To save time, clone the repo on the machine from which you are controlling fleet.
[Unit]
Description=subgun
[Service]
ExecStartPre=-/usr/bin/docker kill subgun-%i
ExecStartPre=-/usr/bin/docker rm subgun-%i
ExecStart=/usr/bin/docker run --rm --name subgun-%i -e SUBGUN_LISTEN=127.0.0.1:8080 -e SUBGUN_LISTS[email protected] -e SUBGUN_API_KEY=<your-sungun-api-key> -p 8080:8080 coreos/subgun
ExecStop=/usr/bin/docker stop subgun-%i
[X-Fleet]
Conflicts=subgun-http@*.service[Unit]
Description=subgun presence service
BindsTo=subgun-http@%i.service
[Service]
ExecStartPre=-/usr/bin/docker kill subgun-presence-%i
ExecStartPre=-/usr/bin/docker rm subgun-presence-%i
ExecStart=/usr/bin/docker run --rm --name subgun-presence-%i -e AWS_ACCESS_KEY=<your-access-key> -e AWS_SECRET_KEY=<your-secret-key> -e AWS_REGION=us-east-1 -e ELB_NAME=bcwaldon-fleet-lb quay.io/coreos/elb-presence
ExecStop=/usr/bin/docker stop subgun-presence-%i
[X-Fleet]
MachineOf=subgun-http@%i.serviceIf you are going to modify these units, be sure you don't copy a docker run command that starts a container in detached mode (-d). Detached mode won't start the container as a child of the unit's pid. This will cause the unit to run for just a few seconds and then exit.
First, load the unit file templates into fleet:
$ fleetctl submit [email protected] [email protected]
$ fleetctl list-unit-files
UNIT HASH DSTATE STATE TMACHINE
[email protected] 08be408 inactive inactive -
[email protected] 5180ed9 inactive inactive -And now, using shell expansion, we can easily launch three instances of each template:
$ fleetctl start subgun-presence@{1..3}.service subgun-http@{1..3}.service
Unit [email protected] launched on 0e0a1f59.../172.17.8.102
Unit [email protected] launched on 30a73182.../172.17.8.103
Unit [email protected] launched on 0e0a1f59.../172.17.8.102
Unit [email protected] launched on 30a73182.../172.17.8.103
Unit [email protected] launched on 610a163d.../172.17.8.101
Unit [email protected] launched on 610a163d.../172.17.8.101
$ fleetctl list-units
UNIT MACHINE ACTIVE SUB
[email protected] 0e0a1f59.../172.17.8.102 active running
[email protected] 30a73182.../172.17.8.103 active running
[email protected] 610a163d.../172.17.8.101 active running
[email protected] 0e0a1f59.../172.17.8.102 active running
[email protected] 30a73182.../172.17.8.103 active running
[email protected] 610a163d.../172.17.8.101 active runningAt this point, our application is deployed!