Expose container DNS to another container? - docker

Using Docker Compose and Traefik, I am trying to have the application container communicate to the solr container and vice versa in a local environment.
Currently, I can access both the application and the solr URL in the browser just fine, but they cannot 'see' or talk to one another internally.
I am new with Docker. Here is a section of my docker compose file with the relevant containers:
php:
image: wodby/drupal-php:$PHP_TAG
container_name: "${PROJECT_NAME}_php"
environment:
PHP_SENDMAIL_PATH: /usr/sbin/sendmail -t -i -S mailhog:1025
DB_HOST: $DB_HOST
DB_USER: $DB_USER
DB_PASSWORD: $DB_PASSWORD
DB_NAME: $DB_NAME
DB_DRIVER: $DB_DRIVER
PHP_FPM_USER: wodby
PHP_FPM_GROUP: wodby
COLUMNS: 80
volumes:
- ./:/var/www/html:cached
solr:
image: wodby/solr:$SOLR_TAG
container_name: "${PROJECT_NAME}_solr"
environment:
SOLR_DEFAULT_CONFIG_SET: $SOLR_CONFIG_SET
SOLR_HEAP: 1024m
labels:
- 'traefik.backend=${PROJECT_NAME}_solr'
- 'traefik.port=8983'
- 'traefik.frontend.rule=Host:solr.${PROJECT_BASE_URL}'
traefik:
image: traefik
container_name: "${PROJECT_NAME}_traefik"
command: -c /dev/null --web --docker --logLevel=INFO
ports:
- '80:80'
- '8983:8983'
volumes:
- /var/run/docker.sock:/var/run/docker.sock
I can access Solr at the given URL, but the application cannot see it at the same URL. I need to be able to do this so it can talk to Solr and have it crawl/etc.
Is there a way to expose them so they can see each other by their hostname?

docker-compose has container DNS resolution built-in. You can expose a specific port on your container to enable access within the docker network, or define port (as you have done for your traefik container) to expose it both within the docker network and externally. In either case, you will be able to access another container by its name (eg. php,solr,or traefik in this case) on the exposed port from another container.

Related

Docker container can't talk to another container

I have a docker compose file set up with 3 separate containers (Flask, Nginx and Solr)
After starting up all 3 run successfully but my Flask application can't connect to my Solr instance and when I run:
wget -S http://localhost:8983/solr/CORE_NAME/select
I get the error "Connecting to localhost (localhost)|127.0.0.1|:8983... failed: Connection refused."
I am fairly new to docker and been around a few different forums looking at this issue but nothing has worked so far. I have tried creating a network also but running into the same issue.
Here is my docker-compose.yml.
version: "2.7"
services:
nginx:
build:
context: .
dockerfile: Dockerfile-nginx
container_name: nginx
ports:
- "80:80"
- "8181:8181"
volumes:
- ./:/opt/ee1
- ee1-logs-volume:/var/log/ee1
- ./:/usr/local/websites/ee1
- sockets-volume:/tmp
depends_on:
- flask
flask:
build:
context: .
dockerfile: Dockerfile-flask
entrypoint: ["/bin/bash", "./system/start-uwsgi-docker.bash"]
container_name: flask
user: root
restart: always
volumes:
- ./:/opt/ee1
- ./ee1config.ini:/opt/ee1config.ini
- ee1jobs-logs-volume:/var/log/ee1
- ./:/usr/local/websites/ee1
- sockets-volume:/tmp
links:
- solr
solr:
build:
context: .
dockerfile: Dockerfile-solr
container_name: solr
volumes:
- data:/var/solr
entrypoint:
- bash
- "-c"
- "precreate-core ee1_1; precreate-core ee1_2; exec solr -f"
ports:
- "8983:8983"
volumes:
sockets-volume: {}
ee1-logs-volume: {}
data:
Every docker container is - network wise - a separate host with it's own IP.
Traffic to localhost or 127.0.0.1 will definitely never leave that container.
So what you need to find out is the IP of the server container (solr) you actually want to talk to, then configure the client container (flask) accordingly. This can be done by e.g. docker inspect. Be aware that upon container restart the IPs can change. You will want to use something like DNS rather than raw IPs.
Since you use docker compose, each container for a service joins the same network and is both reachable by other containers on that network, and discoverable by them at a hostname identical to the container name.
For more details check out
https://docs.docker.com/compose/networking/
https://docs.docker.com/network/

Can't connect to Docker Container on Windows

I have a docker-compose file that looks like this
version: "3"
services:
db:
image: postgres
restart: always
ports:
- "5432:5432"
environment:
POSTGRES_USER: michael
POSTGRES_PASSWORD: pass123
admin:
image: dpage/pgadmin4
restart: always
environment:
PGADMIN_DEFAULT_EMAIL: ${PGADMIN_DEFAULT_EMAIL:-pgadmin4#pgadmin.org}
PGADMIN_DEFAULT_PASSWORD: ${PGADMIN_DEFAULT_PASSWORD:-admin}
PGADMIN_CONFIG_SERVER_MODE: 'False'
ports:
- "5050:5050"
I run docker-compose up -d and I can see my apps running from Docker Desktop. I cannot however connect to my pgadmin instance at port 5050 using localhost. Any ideas?
Docker container of pgAdmin by default runs on port 80 as per the documentation here https://www.pgadmin.org/docs/pgadmin4/latest/container_deployment.html
You are exposing port 5050 through the mapping. Either add a environment variable PGADMIN_LISTEN_PORT to the docker_compose to make pgAdmin run on port 5050
OR
change port mapping to 5050:80 for the pgAdmin service
Check the docker inspect or docker ps results to ensure that you have your port exposed correctly
Try to connect to it using the public IP

Docker-Compose, How To Connect Java Application With Custom Docker Network On Redis Container

I have a java application, that connects through external database through custom docker network
and I want to connect a Redis container.
docker-redis github topic
I tried the following on the application config:
1 localhost:6379
2 app_redis://app_redis:6379
3 redis://app_redis:6379
nothing works on my setup
docker network setup:
docker network create -d bridge --subnet 192.168.0.0/24 --gateway 192.168.0.1 mynet
Connect to a Database Running on Your Docker Host
PS: this might be off-topic, how I can add the network on docker-compose instead of external
docker-compose:
services:
app-kotin:
build: ./app
container_name: app_server
restart: always
working_dir: /app
command: java -jar app-server.jar
ports:
- 3001:3001
links:
- app-redis
networks:
- front
app-redis:
image: redis:5.0.9-alpine
container_name: app-redis
expose:
- 6379
networks:
front:
external:
name: mynet
with the setup above how can I connect through a Redis container?
Both containers need to be on the same Docker network to communicate with each other. The app-kotin container is on the front network, but the app-redis container doesn't have a networks: block and so goes onto an automatically-created default network.
The simplest fix from what you have is to also put the app-redis container on to the same network:
app-redis:
image: redis:5.0.9-alpine
networks:
- front
The Compose service name app-redis will then be usable as a host name, from other containers on the same network.
You can simplify this setup considerably. You don't generally need to manually specify IP configuration for the Docker-private networks. Compose can create the network for you, and in fact it will create a network named default for you. (Networking in Compose discusses this further.) links: and expose: aren't used in modern Docker networking; Compose can provide a default container_name: for you; and you don't need to repeat the working_dir: or command: from the image. Removing all of that would leave you with:
version: '3'
services:
app-kotin:
build: ./app
restart: always
ports:
- '3001:3001'
app-redis:
image: redis:5.0.9-alpine
The server container will be able to use the other container's Compose service name app-redis as a host name, even with this minimal configuration.

How to access docker container using localhost address

I am trying to access a docker container from another container using localhost address.
The compose file is pretty simple. Both containers ports are exposed.
There are no problems when building.
In my host machine I can successfully execute curl http://localhost:8124/ and get a response.
But inside the django_container when trying the same command I get Connection refused error.
I tried adding them in the same network, still result didn't change.
Well if I try to execute with the internal ip of that container like curl 'http://172.27.0.2:8123/' I get the response.
Is this the default behavior? How can I reach clickhouse_container using localhost?
version: '3'
services:
django:
container_name: django_container
build: ./django
ports:
- "8007:8000"
links:
- clickhouse:clickhouse
volumes:
- ./django:/usr/src/run
command: bash /usr/src/run/run.sh
clickhouse:
container_name: clickhouse_container
build: ./clickhouse
ports:
- "9001:9000"
- "8124:8123"
- "9010:9009"
So with this line here - "8124:8123" you're mapping the port of clickhouse container to localhost 8124. Which allows you to access clickhouse from localhost at port 8124.
If you want to hit clickhouse container from within the dockerhost network you have to use the hostname for the container. This is what I like to do:
version: '3'
services:
django:
hostname: djano
container_name: django
build: ./django
ports:
- "8007:8000"
links:
- clickhouse:clickhouse
volumes:
- ./django:/usr/src/run
command: bash /usr/src/run/run.sh
clickhouse:
hostname: clickhouse
container_name: clickhouse
build: ./clickhouse
ports:
- "9001:9000"
- "8124:8123"
- "9010:9009"
If you make the changes like I have made above you should be able to access clickhouse from within the django container like this curl http://clickhouse:8123.
As in #Billy Ferguson's answer, you can visit using localhost in host machine just because: you define a port mapping to route localhost:8124 to clickhouse:8123.
But when from other container(django), you can't. But if you insist, there is a ugly workaround: share host's network namespace with network_mode, but with this the django container will just share all network of host.
services:
django:
hostname: djano
container_name: django
build: ./django
ports:
- "8007:8000"
links:
- clickhouse:clickhouse
volumes:
- ./django:/usr/src/run
command: bash /usr/src/run/run.sh
network_mode: "host"
It depends of config.xml settings. If in config.xml <listen_host> 0.0.0.0</listen_host> you can use clickhouse-client -h your_ip --port 9001

docker-compose.yml container_name and hostname

What is the use of container_name in docker-compose.yml file? Can I use it as hostname which is nothing but the service name in docker-compose.yml file.
Also when I explicitly write hostname under services does it override the hostname represented by service name?
hostname: just sets what the container believes its own hostname is. In the unusual event you got a shell inside the container, it might show up in the prompt. It has no effect on anything outside, and there’s usually no point in setting it. (It has basically the same effect as hostname(1): that command doesn’t cause anything outside your host to know the name you set.)
container_name: sets the actual name of the container when it runs, rather than letting Docker Compose generate it. If this name is different from the name of the block in services:, both names will be usable as DNS names for inter-container communication. Unless you need to use docker to manage a container that Compose started, you usually don’t need to set this either.
If you omit both of these settings, one container can reach another (provided they’re in the same Docker Compose file and have compatible networks: settings) using the name of the services: block and the port the service inside the container is listening in.
version: '3'
services:
redis:
image: redis
db:
image: mysql
ports: [6033:3306]
app:
build: .
ports: [12345:8990]
env:
REDIS_HOST: redis
REDIS_PORT: 6379
MYSQL_HOST: db
MYSQL_PORT: 3306
The easiest answer is the following:
container_name: This is the container name that you see from the host machine when listing the running containers with the docker container ls command.
hostname: The hostname of the container. Actually, the name that you define here is going to the /etc/hosts file:
$ exec -it myserver /bin/bash
bash-4.2# cat /etc/hosts
127.0.0.1 localhost
172.18.0.2 myserver
That means you can ping machines by that names within a Docker network.
I highly suggest set these two parameters the same to avoid confusion.
An example docker-compose.yml file:
version: '3'
services:
database-server:
image: ...
container_name: database-server
hostname: database-server
ports:
- "xxxx:yyyy"
web-server:
image: ...
container_name: web-server
hostname: web-server
ports:
- "xxxx:xxxx"
- "5101:4001" # debug port
you can customize the image name to build & container name during docker-compose up for this, you need to mention like below in docker-compose.yml file.
It will create an image & container with custom names.
version: '3'
services:
frontend_dev:
stdin_open: true
environment:
- CHOKIDAR_USEPOLLING=true
build:
context: .
dockerfile: Dockerfile.dev
image: "mycustomname/sample:v1"
container_name: mycustomname_sample_v1
ports:
- '3000:3000'
volumes:
- /app/node_modules
- .:/app

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