concourse/tsa

tsa

controls worker authentication within concourse

by stuckincustoms

reporting issues and requesting features

please report all issues and feature requests in concourse/concourse

about

TSA is the way workers securely register to join a Concourse deployment. It provides authentication and transport encryption (if required). Worker machines can ssh into TSA with a custom command to register or have traffic forwarded to them. Once an SSH session has been established then TSA begins to automatically heartbeat information about the worker into the ATC's pool.

The main advantage that this provides over the old style of registration is that Workers no longer need to be internet routable in order to have the ATC reach them. They open a reverse tunnel through the TSA which, when collocated with ATC, is far more likely to be easily routable. This also allows for simpler setup and better security as before you either had to expose your Garden server publicly or set up some interesting custom security if the workers and ATC were not in the same private network.

usage

First, create two new SSH keys:

$ ssh-keygen -t rsa -f host_key
$ ssh-keygen -t rsa -f worker_key

Next, let's create an authorized keys file so that our workers are able to authenticate with us without providing a password:

cat worker_key.pub > authorized_keys

Now to start tsa itself:

tsa \
  --peer-address $PEER_ADDRESS \
  --host-key ./host_key \
  --authorized-keys ./authorized_keys \
  --session-signing-key $SIGNING_KEY \
  --atc-url $ATC_URL

The variables here should be set to:

Variable	Description
$PEER_ADDRESS	The host or IP where this machine can be reached by the ATC for the purpose of forwarding traffic to remote workers.
$SIGNING_KEY	RSA key used to sign the tokens used when communicating to the ATC.
$ATC_URL	ATC URL reachable by the TSA (e.g. https://ci.concourse-ci.org).

forwarding workers

In order to have a worker on a remote network register with tsa and have its traffic forwarded you can run the following command:

ssh -p 2222 $TSA_HOST \
  -i worker_key \
  -o UserKnownHostsFile=host_key.pub \
  -R0.0.0.0:7777:127.0.0.1:7777 \
  -R0.0.0.0:7788:127.0.0.1:7788 \
  forward-worker \
    --garden 0.0.0.0:7777 \
    --baggageclaim 0.0.0.0:7788 \
  < worker.json

Note that in this case you should always have Garden and BaggageClaim listen on 127.0.0.1 so that they're not exposed to the outside world. For this reason there is no $GARDEN_ADDR or $BAGGAGECLAIM_URL.

The worker.json file should contain the following:

{
    "platform": "linux",
    "tags": []
}