accessing a docker container from another container

Question

i created two docker containers based on two different images. one of db and another for webserver. both containers are running on my mac osx.

i can access db container from host machine and same way can access webserver from host machine.

however, how do i access db connection from webserver?

the way i started db container is

docker run --name oracle-db -p 1521:1521 -p 5501:5500 oracle/database:12.1.0.2-ee

I started wls container as

docker run --name oracle-wls -p 7001:7001 wls-image:latest

I can access db on host by connecting to

sqlplus scott/welcome1@//localhost:1521/ORCLCDB

I can access wls on host as

http://localhost:7001/console

User · Answer

Using docker-compose  services are exposed to each other by name by default  Docs  You could also specify an alias like   version   2 1  services    mongo      image  mongo 3 2 11   redis      image  redis 3 2 10   api      image  some-image     depends on        - mongo       - solr     links        -  mongo mongo openconceptlab org        -  solr solr openconceptlab org        -  some-service some-alias    And then access the service using the specified alias as a host name  e g mongo openconceptlab org for mongo in this case

User · Answer

You will have to access db through the ip of host machine, or if you want to access it via localhost:1521, then run webserver like -

docker run --net=host --name oracle-wls wls-image:latest

See here

User · Answer

It s easy  If you have two or more running container  complete next steps   docker network create myNetwork docker network connect myNetwork web1 docker network connect myNetwork web2   Now you connect from web1 to web2 container or the other way round    Use the internal network IP addresses which you can find by running   docker network inspect myNetwork   Note that only internal IP addresses and ports are accessible to the containers connected by the network bridge    So for example assuming that web1 container was started with  docker run -p 80 8888 web1  meaning that its server is running on port 8888 internally   and inspecting myNetwork shows that web1 s IP is 172 0 0 2  you can connect from web2 to web1 using curl 172 0 0 2 8888

User · Answer

Easiest way is to use --link  however the newer versions of docker are moving away from that and in fact that switch will be removed soon  The link below offers a nice how too  on connecting two containers  You can skip the attach portion  since that is just a useful how to on adding items to images  https   deis com blog 2016 connecting-docker-containers-1  The part you are interested in is the communication between two containers  The easiest way  is to refer to the DB container by name from the webserver container  Example  you named the db container db1 and the webserver container web0  The containers should both be on the bridge network  which means the web container should be able to connect to the DB container by referring to it s name  So if you have a web config file for your app  then for DB host you will use the name db1  if you are using an older version of docker  then you should use --link  Example  Step 1  docker run --name db1 oracle database 12 1 0 2-ee then when you start the web app  use  Step 2  docker run --name web0 --link db1 webapp webapp 3 0 and the web app will be linked to the DB  However  as I said the --link switch will be removed soon  I d use docker compose instead  which will build a network for you  However  you will need to download docker compose for your system  https   docs docker com compose install  prerequisites an example setup is like this  file name is base yml version   quot 2 quot  services    webserver      image   quot moodlehq moodle-php-apache 7 1     depends on        - db     volumes        -  quot  var www html  var www html quot        -  quot  home some user web apache2 faildumps conf  etc apache2 conf-enabled apache2 faildumps conf quot      environment        MOODLE DOCKER DBTYPE  pgsql       MOODLE DOCKER DBNAME  moodle       MOODLE DOCKER DBUSER  moodle       MOODLE DOCKER DBPASS   quot m 0dl3ing quot        HTTP PROXY   quot   HTTP PROXY  quot        HTTPS PROXY   quot   HTTPS PROXY  quot        NO PROXY   quot   NO PROXY  quot    db      image  postgres 9     environment        POSTGRES USER  moodle       POSTGRES PASSWORD   quot m 0dl3ing quot        POSTGRES DB  moodle       HTTP PROXY   quot   HTTP PROXY  quot        HTTPS PROXY   quot   HTTPS PROXY  quot        NO PROXY   quot   NO PROXY  quot   this will name the network a generic name  I can t remember off the top of my head what that name is  unless you use the --name switch  IE docker-compose --name setup1 up base yml NOTE  if you use the --name switch  you will need to use it when ever calling docker compose  so docker-compose --name setup1 down this is so you can have more then one instance of webserver and db  and in this case  so docker compose knows what instance you want to run commands against  and also so you can have more then one running at once  Great for CI CD  if you are running test in parallel on the same server  Docker compose also has the same commands as docker so docker-compose --name setup1 exec webserver do some command best part is  if you want to change db s or something like that for unit test you can include an additional  yml file to the up command and it will overwrite any items with similar names  I think of it as a key  gt value replacement  Example  db yml version   quot 2 quot  services    webserver      environment        MOODLE DOCKER DBTYPE  oci       MOODLE DOCKER DBNAME  XE   db      image  moodlehq moodle-db-oracle  Then call docker-compose --name setup1 up base yml db yml This will overwrite the db  with a different setup  When needing to connect to these services from each container  you use the name set under service  in this case  webserver and db  I think this might actually be a more useful setup in your case  Since you can set all the variables you need in the yml files and just run the command for docker compose when you need them started  So a more start it and forget it setup  NOTE  I did not use the --port command  since exposing the ports is not needed for container- gt container communication  It is needed only if you want the host to connect to the container  or application from outside of the host  If you expose the port  then the port is open to all communication that the host allows  So exposing web on port 80 is the same as starting a webserver on the physical host and will allow outside connections  if the host allows it  Also  if you are wanting to run more then one web app at once  for whatever reason  then exposing port 80 will prevent you from running additional webapps if you try exposing on that port as well  So  for CI CD it is best to not expose ports at all  and if using docker compose with the --name switch  all containers will be on their own network so they wont collide  So you will pretty much have a container of containers  UPDATE  After using features further and seeing how others have done it for CICD programs like Jenkins  Network is also a viable solution  Example  docker network create test network  The above command will create a  quot test network quot  which you can attach other containers too  Which is made easy with the --network switch operator  Example  docker run       --detach       --name db1       --network test network       -e MYSQL ROOT PASSWORD  quot   DBPASS  quot        -e MYSQL DATABASE  quot   DBNAME  quot        -e MYSQL USER  quot   DBUSER  quot        -e MYSQL PASSWORD  quot   DBPASS  quot        --tmpfs  var lib mysql rw       mysql 5  Of course  if you have proxy network settings you should still pass those into the containers using the  quot -e quot  or  quot --env-file quot  switch statements  So the container can communicate with the internet  Docker says the proxy settings should be absorbed by the container in the newer versions of docker  however  I still pass them in as an act of habit  This is the replacement for the  quot --link quot  switch which is going away  Once the containers are attached to the network you created you can still refer to those containers from other containers using the  name  of the container  Per the example above that would be db1  You just have to make sure all containers are connected to the same network  and you are good to go  For a detailed example of using network in a cicd pipeline  you can refer to this link  https   git in moodle com integration nightlyscripts blob master runner master run sh Which is the script that is ran in Jenkins for a huge integration tests for Moodle  but the idea example can be used anywhere  I hope this helps others

[docker] accessing a docker container from another container

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