Unable connect from one container to another - docker

Question

I have a Dockerfile and docker-compose.yml file set up, but not sure if they are correct and I am unable to run it without an error.
My Dockerfile is:
FROM golang:1.14-alpine
RUN mkdir /app
ADD . /app
WORKDIR /app
RUN go get
RUN go run server.go
and my compose.yml is:
version: "3.5"
services:
elasticsearch:
container_name: "elasticsearch"
image: docker.elastic.co/elasticsearch/elasticsearch:7.8.0
ports:
- 9200:9200
gqlgen:
container_name: "gqlgen"
build: ./
restart: "on-failure"
ports:
- "8080:8080"
depends_on:
- elasticsearch
This is how the root of my folder looks like:
I tried to run: docker-compose up from the root directory and this is what I get:
panic: Get "http://127.0.0.1:9200/": dial tcp 127.0.0.1:9200: connect: connection refused
I think I am doing my setup wrong.
UPDATE:
Based on suggestions and more stuff that I read online, I changed my DOCKERFILE as:
FROM golang:1.14-alpine
RUN mkdir /app
ADD . /app
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN go build -o server .
CMD ["./server"]
and compose file:
version: "3.5"
services:
elasticsearch:
container_name: "elasticsearch"
image: docker.elastic.co/elasticsearch/elasticsearch:7.8.0
environment:
- node.name=elasticsearch
- cluster.name=es-docker-cluster
- bootstrap.memory_lock=true
- cluster.initial_master_nodes=elasticsearch
- "ES_JAVA_OPTS=-Xms512m -Xmx512m"
ulimits:
memlock:
soft: -1
hard: -1
ports:
- 9200:9200
golang:
container_name: "golang"
build:
context: .
dockerfile: Dockerfile
ports:
- "8080:8080"
restart: unless-stopped
depends_on:
- elasticsearch
and it builds correctly now.
But same issue with running docker-compose up.
panic: Get "http://elasticsearch:9200/": dial tcp 172.18.0.2:9200: connect: connection refused

Answer 1

You have a problem because you address Elasticsearch incorrectly.
Inside docker container 127.0.0.1 refers to the container itself, so your app is trying to find Elasticsearch where there isn't one.
The correct way to reference one docker container from another is by using docker container name. So in your case, it would be using name: elasticsearch.
Edit:
There is another issue with your configuration.
You miss some vital elements of Elasticsearch configuration.
Here you have snippet with minimal configuration for a single node Elasticsearch cluster.
services:
elasticsearch:
container_name: "elasticsearch"
image: docker.elastic.co/elasticsearch/elasticsearch:7.8.0
environment:
- node.name=elasticsearch
- cluster.name=es-docker-cluster
- bootstrap.memory_lock=true
- cluster.initial_master_nodes=elasticsearch
- "ES_JAVA_OPTS=-Xms512m -Xmx512m"
ulimits:
memlock:
soft: -1
hard: -1
ports:
- 9200:9200
All I have written before is still valid. After modifying docker-compose your last version which refers to Elasticsearch via http://elasticsearch:9200 should work fine.
Edit:
As #David Maze pointed out there is a third issue in your example.
Instead of RUN go run server.go you should have CMD go run server.go.
What you are doing is running your app during your build, when you want to run your app inside the container.
The more conventional approach would be to build app, instead of copying the source, copying the binary to the container and running the binary inside the container.
Here you have some information about that: https://medium.com/travis-on-docker/multi-stage-docker-builds-for-creating-tiny-go-images-e0e1867efe5a

Answer 2

So the above action to replace localhost with elasticsearch is correct.
But this it should happen only when you are starting your up with docker-compose.
Do not attempt to call elasticsearch from your IDE using elasticearch instead of host.
I suggest to make the host of elasticsearch configurable and for local configuration keep localhost, but you can override it in docker-compose file.
version: "3.5"
services:
elasticsearch:
container_name: "elasticsearch"
image: docker.elastic.co/elasticsearch/elasticsearch:7.8.0
environment:
- node.name=elasticsearch
- cluster.name=es-docker-cluster
- bootstrap.memory_lock=true
- cluster.initial_master_nodes=elasticsearch
- "ES_JAVA_OPTS=-Xms512m -Xmx512m"
ulimits:
memlock:
soft: -1
hard: -1
ports:
- 9200:9200
golang:
container_name: "golang"
build:
context: .
dockerfile: Dockerfile
ports:
- "8080:8080"
restart: unless-stopped
depends_on:
- elasticsearch
environment:
- ELASTICSEARCH_HOST: elasticsearch
Where ELASTICSEARCH_HOST is a variable that you use in your project