DC/OS comes with a set of powerful yet un-opinionated service discovery mechanisms. While powerful, it can sometimes be hard for newcomers to quickly get results, so here a few tips and tricks in the following.
- Many shell commands below assume you've got jq installed.
- All bash shell commands below assume that you've added your private SSH key already; if you haven't done this yet do the following:
$ ssh-add ~/.ssh/MYPRIVATEKEY
Let's say you have a Marathon app with the app ID /example and want to know on the public routable IP address it is running (if it's on a public node):
$ export APP_NODE=$(echo "curl -s ifconfig.ca" | dcos node ssh --master-proxy --mesos-id=$(dcos task --json | jq --raw-output '.[] | select(.name == "example") | .slave_id') 2>/dev/null)
To get the cluster-internal IP address of the public node:
$ export PUBLIC_NODE_INTERNAL_IP=$(dcos node --json | jq "map(select(.attributes.public_ip).hostname)" | grep \" | cut -d"\"" -f 2)
To get the public Internet-routable IP address of the public node:
$ export PUBLIC_NODE_PUBLIC_IP=$(echo "curl -s ifconfig.ca" | dcos node ssh --master-proxy --mesos-id=$(dcos node --json | jq --raw-output '.[] | select(.reserved_resources.slave_public != null) | .id') 2>/dev/null)
To get the (cluster-internal) IP address and port of a Marathon app:
$ export APP_ENDPOINT=$(dcos marathon task list --json | jq "map(select(.appId==\"/peek\").host, select(.appId==\"/peek\").ports)")
Using the same base command, manual:
$ dcos marathon task list
APP HEALTHY STARTED HOST ID
/example True 2016-04-22T13:00:57.458Z 10.0.3.34 example.3459106a-088a-11e6-ba3b-9eefd772c507
$ dcos marathon task show example.3459106a-088a-11e6-ba3b-9eefd772c507 | jq .host,.ports
"10.0.3.34"
[
31105
]
Or, alternatively, using a different sub-command:
$ export APP_ENDPOINT=$(dcos marathon app show peek | jq .tasks[0].host,.tasks[0].ports[0])
Assuming you want a Marathon app with the ID /example and you have dig installed. Then you can—from within the cluster, that is, after SSHing into a node—do the following:
$ app_port=$(dig _peek._tcp.marathon.mesos SRV | grep ^_peek._tcp.marathon.mesos. | cut -d " " -f 4)
$ app_ip=$(dig _peek._tcp.marathon.mesos SRV | grep ^$(dig _peek._tcp.marathon.mesos SRV | grep ^_peek._tcp.marathon.mesos. | cut -d " " -f 5) | cut -d " " -f 3 | cut -d$'\t' -f 3)
$ export APP_ENDPOINT=$app_ip:$app_port
type SRVRecord struct {
Service string
Host string
IP string
Port string
}
func serviceDiscovery(lookup string) string {
mesosdns := "http://leader.mesos:8123" // the Mesos-DNS HTTP API within the cluster
query := "_" + lookup + "._tcp.marathon.mesos."
resp, err := http.Get(mesosdns + "/v1/services/" + query)
if err != nil {
log.Fatalf("Can't look up my address due to %v", err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
log.Fatalf("Error reading response from Mesos-DNS due to %v", err)
}
var srvrecords []SRVRecord
err = json.Unmarshal(body, &srvrecords)
if err != nil {
log.Fatalf("Error decoding JSON object due to %v", err)
}
return "http://" + srvrecords[0].Host + ":" + srvrecords[0].Port
}
- front-end of the m-shop: See the example.
- mesosdns-cli: A CLI for querying Mesos DNS service names.
- mesosdns-client: A simple client for Mesos DNS which makes it possible to receive actual endpoints from Mesos service names.
- mesosdns-http-agent: A http.Agent which makes it possible to consume Mesos service resources by simply using the Mesos DNS service names.
- tobilg/mesosdns-resolver: A bash script to resolve Mesos DNS SRV records to actual host:port endpoints
See the mc project.