docker stack communicate between containers - docker

Question

I'm trying to setup a swarm using docker but I'm having issues with communicating between containers.
I have cluster with 5 nodes. 1 manager and 4 workers.
3 apps: redis, splash, myapp
myapp has to be on the 4 workers
redis, splash just on the manager
myapp has to be able to communicate with redis and splash
I tried using the container name but its not working. It resolves the container name to different IPs.
ping splash # return a different ip than the container actually has
I am deploying running the swarm using docker stack
docker stack deploy -c docker-stack.yml myapp
Linking container between them also doesn't work.
Any ideas ? Am I missing something ?
root#swarm-manager:~# docker version
Client:
Version: 17.09.0-ce
API version: 1.32
Go version: go1.8.3
Git commit: afdb6d4
Built: Tue Sep 26 22:42:18 2017
OS/Arch: linux/amd64
Server:
Version: 17.09.0-ce
API version: 1.32 (minimum version 1.12)
Go version: go1.8.3
Git commit: afdb6d4
Built: Tue Sep 26 22:40:56 2017
OS/Arch: linux/amd64
Experimental: false
docker-stack.yml contains:
version: "3"
services:
splash:
container_name: splash
image: scrapinghub/splash
ports:
- 8050:8050
- 5023:5023
deploy:
mode: global
placement:
constraints:
- node.role == manager
redis:
container_name: redis
image: redis
ports:
- 6379:6379
deploy:
mode: global
placement:
constraints:
- node.role == manager
myapp:
container_name: myapp
image: myapp_image:latest
environment:
REDIS_ENDPOINT: redis:6379
SPLASH_ENDPOINT: splash:8050
deploy:
mode: global
placement:
constraints:
- node.role == worker
entrypoint:
- ping google.com
---- EDIT ----
I tried with curl also. Didn't work.
docker stack deploy -c docker-stack.yml myapp
Creating network myapp_default
Creating service myapp_splash
Creating service myapp_redis
Creating service myapp_myapp
curl http://myapp_splash:8050
curl: (7) Failed to connect to myapp_splash port 8050: No route to host
curl http://splash:8050
curl: (7) Failed to connect to splash port 8050: No route to host
What worked is getting the actual container name of splash, which is some random generated string.
curl http://myapp_splash.d7bn0dpei9ijpba4q41vpl4zz.tuk1cimht99at9g0au8vj9lkz:8050
But this doesn't really help me.

Answer 1

Ping is not the proper tool to try and connect services. For some reason it doesn't work with docker networks. Try curl http://serviceName instead.
Other than that: Containers can't be named when using stack deploy, instead your service name is used (which coincidentally is the same) to access another service.

Answer 2

I manage to get it working using curl http://tasks.splash:8050 or http://tasks.myapp_splash:8050.
I don't know whats is causing this issue though. Feel free to comment with an answer.

Answer 3

It seems that containers in stack named tasks.<service name> so the command ping tasks.myservice works for me!
Itersting point to note that names like <stackname>_<service name> will also resolve and ping'able but IP address is incorrect. This is frustarating.
(For exmple if you do docker stack deploy -c my.yml AA you'll get name like AA_myservice which will resolve to incorrect addreses)
To add to above answer. From network point of view curl and ping do the same things. Both will try to resolve name passed to them and then curl will try to connect using specified protocol (http is the example above) and ping will send ICMP echo requests.