I have to consume an external rest API(using restTemplate.exchange) with Spring Boot. My rest API is running on port 8083 with URL http://localhost:8083/myrest (Docker command : docker run -p 8083:8083 myrest-app)
External API is available in form of public docker image and after running below command , I am able to pull and run it locally.
docker pull dockerExternalId/external-rest-api docker
run -d -p 3000:3000 dockerExternalId/external-rest-api
a) If I enter external rest API URL, for example http://localhost:3000/externalrestapi/testresource directly in chrome, then I get valid JSON data.
b) If I invoke it with myrest application from eclipse(Spring Boot Application), still I am getting valid JSON Response. (I am using Windows Platform to test this)
c) But if I run it on Docker and execute myrest service (say http://localhost:8083/myrest), then i am facing java.net.ConnectException: Connection refused
More details :
org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://localhost:3000/externalrestapi/testresource": Connection refused (Connection refused); nested exception is java.net.ConnectException: Connection refused (Connection refused)
P.S - I am using Docker on Windows.
# The problem
You run with:
docker run -p 8083:8083 myrest-app
But you need to run like:
docker run --network "host" --name "app" myrest-app
So passing the flag --network with value host will allow you container to access your computer network.
Please ignore my first approach, instead use a better alternative that does not expose the container to the entire host network... is possible to make it work, but is not a best practice.
A Better Alternative
Create a network to be used by both containers:
docker network create external-api
Then run both containers with the flag --network external-api.
docker run --network "external-api" --name "app" -p 8083:8083 myrest-app
and
docker run -d --network "external-api" --name "api" -p 3000:3000 dockerExternalId/external-rest-api
The use of flag -p to publish the ports for the api container are only necessary if you want to access it from your computers browser, otherwise just leave them out, because they aren't needed for 2 containers to communicate in the external-api network.
TIP: docker pull is not necessary, once docker run will try to pull the image if does not found it in your computer.
Let me know how it went...
Call the External API
So in both solutions I have added the --name flag so that we can reach the other container in the network.
So to reach the external api from my rest app you need to use the url http://api:3000/externalrestapi/testresource.
Notice how I have replaced localhost by api that matches the value for --name flag in the docker run command for your external api.
From your myrest-app container if you try to access http://localhost:3000/externalrestapi/testresource, it will try to access 3000 port of the same myrest-app container.
Because each container is a separate running Operating System and it has its own network interface, file system, etc.
Docker is all about Isolation.
There are 3 ways by which you can access an API from another container.
Instead of localhost, provide the IP address of the external host machine (i.e the IP address of your machine on which docker is running)
Create a docker network and attach these two containers. Then you can provide the container_name instead of localhost.
Use --link while starting the container (deprecated)
I like to use scrapyRT to connect all my scraper spiders to the Angular front-end.
The documentation recommends to run in it in production as follows:
docker run -p 9080:9080 -tid -v /home/user/quotesbot:/scrapyrt/project scrapinghub/scrapyrt
This will expose port 9080 to the outside world.
I'm concerned about the safety of this.
How can I properly secure this to avoid bots visiting the end points?
If Scrapyrt is running on the same machine as your frontend, you could make Scrapyrt listen only on localhost:
docker run -p 9080:9080 -tid -v /home/user/quotesbot:/scrapyrt/project scrapinghub/scrapyrt -i 127.0.0.1
That way it will be accessible only from that machine (e.g. from the frontend application).
Otherwise use firewall to allow communication from your frontend machine only.
I need to configure docker as service in my CentOs machine.
It's set up and works fine. However I need to add this host -H unix:///var/run/docker.sock.
How can I set this parameter up in order to each time the service is started this option is reached.
From the docker daemon configuration page, those options should go in a /etc/systemd/system/docker.service.d/docker.conf config file.
For instance:
Override the ExecStart configuration from your docker.conf file to customize the docker daemon.
To modify the ExecStart configuration you have to specify an empty configuration followed by a new one as follows:
[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H fd:// -D --tls=true --tlscert=/var/docker/server.pem --tlskey=/var/docker/serverkey.pem -H tcp://192.168.59.3:2376
I've created a kubenetes cluster on my Mac with docker-machine, following the documentation here:
http://kubernetes.io/docs/getting-started-guides/docker/
I can access the normal api from inside the instance on 127.0.0.1:8080, but I want to access it externally from my macbook. I know there is a secure port :6443, but I'm unsure how to set up the credentials to access this port.
There are lots of instructions on how to do it on custom installs of kubernetes, but I don't know how to do it inside the docker containers I'm running.
Likely, you will want to use Virtual Box's port forwarding capabilities. An example from the documentation:
VBoxManage modifyvm "MyVM" --natpf1 "k8srule,tcp,,6443,,6443"
This forwards port 6443 on all hosts interfaces to port 6443 of the guest. Port forwarding can also be configured through the VirtualBox UI.
It's like a workaround but most of the time, I think KubeOnDocker setup is for developper that don't need the credentials mecanism :
When you start the KubeOnDocker, --config=/etc/kubernetes/manifests point to master.json. If you look the apiserver start command, you will see that --insecure-bind-address is 127.0.0.1. If you use --config=/etc/kubernetes/manifests-multi it will point to master-multi.json, --insecure-bind-address will be 0.0.0.0 and the apiserver will be accessible from everywhere.
Note that you will need to start etcd with manifests-multi.
# Not tested start
docker run \
-d \
--net=host \
gcr.io/google_containers/etcd:2.2.1 \
/usr/local/bin/etcd \
--listen-client-urls=http://127.0.0.1:4001 \
--advertise-client-urls=http://127.0.0.1:4001 \
--data-dir=/var/etcd/data
I have a few Docker containers running like:
Nginx
Web app 1
Web app 2
PostgreSQL
Since Nginx needs to connect to the web application servers inside web app 1 and 2, and the web apps need to talk to PostgreSQL, I have linkages like this:
Nginx --- link ---> Web app 1
Nginx --- link ---> Web app 2
Web app 1 --- link ---> PostgreSQL
Web app 2 --- link ---> PostgreSQL
This works pretty well at first. However, when I develop a new version of web app 1 and web app 2, I need to replace them. What I do is remove the web app containers, set up new containers and start them.
For the web app containers, their IP addresses at first would be something like:
172.17.0.2
172.17.0.3
And after I replace them, they will have new IP addresses:
172.17.0.5
172.17.0.6
Now, those exposed environment variables in the Nginx container are still pointing to the old IP addresses. Here comes the problem. How do I replace a container without breaking linkage between containers? The same issue will also happen to PostgreSQL. If I want to upgrade the PostgreSQL image version, I certainly need to remove it and run the new one, but then I need to rebuild the whole container graph, so this is not ideal for real-life server operation.
The effect of --link is static, so it will not work for your scenario (there is currently no re-linking, although you can remove links).
We have been using two different approaches at dockerize.it to solve this, without links or ambassadors (although you could add ambassadors too).
1) Use dynamic DNS
The general idea is that you specify a single name for your database (or any other service) and update a short-lived DNS server with the actual IP as you start and stop containers.
We started with SkyDock. It works with two docker containers, the DNS server and a monitor that keeps it updated automatically. Later we moved to something more custom using Consul (also using a dockerized version: docker-consul).
An evolution of this (which we haven't tried) would be to setup etcd or similar and use its custom API to learn the IPs and ports. The software should support dynamic reconfiguration too.
2) Use the docker bridge ip
When exposing the container ports you can just bind them to the docker0 bridge, which has (or can have) a well known address.
When replacing a container with a new version, just make the new container publish the same port on the same IP.
This is simpler but also more limited. You might have port conflicts if you run similar software (for instance, two containers can not listen on the 3306 port on the docker0 bridge), etcétera… so our current favorite is option 1.
Links are for a specific container, not based on the name of a container. So the moment you remove a container, the link is disconnected and the new container (even with the same name) will not automatically take its place.
The new networking feature allows you to connect to containers by
their name, so if you create a new network, any container connected to
that network can reach other containers by their name. Example:
1) Create new network
$ docker network create <network-name>
2) Connect containers to network
$ docker run --net=<network-name> ...
or
$ docker network connect <network-name> <container-name>
3) Ping container by name
docker exec -ti <container-name-A> ping <container-name-B>
64 bytes from c1 (172.18.0.4): icmp_seq=1 ttl=64 time=0.137 ms
64 bytes from c1 (172.18.0.4): icmp_seq=2 ttl=64 time=0.073 ms
64 bytes from c1 (172.18.0.4): icmp_seq=3 ttl=64 time=0.074 ms
64 bytes from c1 (172.18.0.4): icmp_seq=4 ttl=64 time=0.074 ms
See this section of the documentation;
Note: Unlike legacy links the new networking will not create environment variables, nor share environment variables with other containers.
This feature currently doesn't support aliases
You can use an ambassador container. But do not link the ambassador container to your client, since this creates the same problem as above. Instead, use the exposed port of the ambassador container on the docker host (typically 172.17.42.1). Example:
postgres volume:
$ docker run --name PGDATA -v /data/pgdata/data:/data -v /data/pgdata/log:/var/log/postgresql phusion/baseimage:0.9.10 true
postgres-container:
$ docker run -d --name postgres --volumes-from PGDATA -e USER=postgres -e PASS='postgres' paintedfox/postgresql
ambassador-container for postgres:
$ docker run -d --name pg_ambassador --link postgres:postgres -p 5432:5432 ctlc/ambassador
Now you can start a postgresql client container without linking the ambassador container and access postgresql on the gateway host (typically 172.17.42.1):
$ docker run --rm -t -i paintedfox/postgresql /bin/bash
root#b94251eac8be:/# PGHOST=$(netstat -nr | grep '^0\.0\.0\.0 ' | awk '{print $2}')
root#b94251eac8be:/# echo $PGHOST
172.17.42.1
root#b94251eac8be:/#
root#b94251eac8be:/# psql -h $PGHOST --user postgres
Password for user postgres:
psql (9.3.4)
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)
Type "help" for help.
postgres=#
postgres=# select 6*7 as answer;
answer
--------
42
(1 row)
bpostgres=#
Now you can restart the ambassador container whithout having to restart the client.
If anyone is still curious, you have to use the host entries in /etc/hosts file of each docker container and should not depend on ENV variables as they are not updated automatically.
There will be a host file entry for each of the linked container in the format LINKEDCONTAINERNAME_PORT_PORTNUMBER_TCP etc..
The following is from docker docs
Important notes on Docker environment variables
Unlike host entries in the /etc/hosts file, IP addresses stored in the
environment variables are not automatically updated if the source
container is restarted. We recommend using the host entries in
/etc/hosts to resolve the IP address of linked containers.
These environment variables are only set for the first process in the
container. Some daemons, such as sshd, will scrub them when spawning
shells for connection.
This is included in the experimental build of docker 3 weeks ago, with the introduction of services: https://github.com/docker/docker/blob/master/experimental/networking.md
You should be able to get a dynamic link in place by running a docker container with the --publish-service <name> arguments. This name will be accessible via the DNS. This is persistent on container restarts (as long as you restart the container with the same service name that is of course)
You may use dockerlinks with names to solve this.
Most basic setup would be to first create a named database container :
$ sudo docker run -d --name db training/postgres
then create a web container connecting to db :
$ sudo docker run -d -P --name web --link db:db training/webapp python app.py
With this, you don't need to manually connect containers with their IP adresses.
with OpenSVC approach, you can workaround by :
use a service with its own ip address/dns name (the one your end users will connect to)
tell docker to expose ports to this specific ip address ("--ip" docker option)
configure your apps to connect to the service ip address
each time you replace a container, you are sure that it will connect to the correct ip address.
Tutorial here => Docker Multi Containers with OpenSVC
don't miss the "complex orchestration" part at the end of tuto, which can help you start/stop containers in the correct order (1 postgresql subset + 1 webapp subset + 1 nginx subset)
the main drawback is that you expose webapp and PostgreSQL ports to public address, and actually only the nginx tcp port need to be exposed in public.
You could also try the ambassador method of having an intermediary container just for keeping the link intact... (see https://docs.docker.com/articles/ambassador_pattern_linking/ ) for more info
You can bind the connection ports of your images to fixed ports on the host and configure the services to use them instead.
This has its drawbacks as well, but it might work in your case.
Another alternative is to use the --net container:$CONTAINER_ID option.
Step 1: Create "network" containers
docker run --name db_net ubuntu:14.04 sleep infinity
docker run --name app1_net --link db_net:db ubuntu:14.04 sleep infinity
docker run --name app2_net --link db_net:db ubuntu:14.04 sleep infinity
docker run -p 80 -p 443 --name nginx_net --link app1_net:app1 --link app2_net:app2 ubuntu:14.04 sleep infinity
Step 2: Inject services into "network" containers
docker run --name db --net container:db_net pgsql
docker run --name app1 --net container:app1_net app1
docker run --name app2 --net container:app1_net app2
docker run --name nginx --net container:app1_net nginx
As long as you do not touch the "network" containers, the IP addresses of your links should not change.
Network-scoped alias is what you need is this case. It's a rather new feature, which can be used to "publish" a container providing a service for the whole network, unlike link aliases accessible only from one container.
It does not add any kind of dependency between containers — they can communicate as long as both are running, regardless of restarts and replacement and launch order. It uses DNS internally, I believe, instead of /etc/hosts
Use it like this: docker run --net=some_user_definied_nw --net-alias postgres ... and you can connect to it using that alias from any container on the same network.
Does not work on the default network, unfortunately, you have to create one with docker network create <network> and then use it with --net=<network> for every container (compose supports it as well).
In addition to container being down and hence unreachable by alias multiple containers can also share an alias in which case it's not guaranteed that it will be resolved to the right one. But in some case that can help with seamless upgrade, probably.
It's all not very well documented as of yet, hard to figure out just by reading the man page.