How to Connect to Your Docker Container Inside Jelastic Cloud

| June 16, 2016

Docker containers integration within Jelastic Cloud has become one of the most important and demanded services, offered by a Platform. And striving to help you to get the maximum outcome from this technology usage, we are regular providing the related guides and tips at our blog. In most cases, they describe some complex solutions (e.g. building DevOps Pipeline for Dockers CD inside Private Cloud), but this time, we’ve decided to return to the basics, which may be a point of interest for both beginners and intermediate developers.

As you’ve probably guessed from the title, today we’ll try to fully observe and explain the ways of connecting to your Docker container at Jelastic, considering both internal and external possibilities.Connect to Docker in Jelastic

So, if you are just learning how to work with your Docker-based application or, probably, have met any difficulties with this while hosting it at Jelastic, the guide below will help you to get started. Within it, we’ll show you where to find the very basic container information that is required for connection and a few quick tips on how this operation can be actually performed.

Internal Connection

Each Docker container at Jelastic automatically gets a unique internal domain name and internal IP address right after creation. These ones can be used to access containers in confines of a single Cloud, i.e. to connect them with each other via the platform’s internal network.

1. The very first option you need to consider in case of the necessity to set up interconnection between your containers is the embedded functionality of Dockers linking. It allows to connect containers from different layers within a single environment to securely transfer environment variables information from source Docker image to the recipient without exposing any ports externally.

For that, you just need to select the required layer and specify an alias for the connection denomination (whilst all of the appropriate variables will get the corresponding prefix according to it):Docker layer setting in Jelastic

Don’t forget to Save and Apply the changes you’ve made.

After that, you may refer to the Variables section of your Docker container settings and adjust any of them separately upon the necessity. Herewith, changing of the environment variable’s value for a container, that is already linked to another one, will also cause its automatic update in a container this link was applied to.

2. In case you need to establish internal connection of another type (i.e. which requires some manual adjustments via the comprised configuration files), you’ll need to know the exact container domain name or IP address it can be accessed through the platform’s internal network.

The appropriate information can be observed in two ways:

  • Through the email notification you receive after environment creation. The corresponding internal domain name and IP address are to be listed within the section with container admin data:

Access to Docker in Jelastic

Here, containers’ domain name is shown at the Access URL string and its internal IP address - within the IP line below.

  • At the Jelastic dashboard, the same data can be found in the following ways:

- Click the Open in browser button next to the Docker container you’re interested in for the required node to be opened in the new browser tab, so you can easily copy its domain from the address bar
Open in browser in Jelastic

Or, just right-click on the domain string under the environment name (circled above) and copy the provided link.

- The internal IP address of the node can be viewed through expanding the Additionally list for the required container, as it is shown in the image below

IP address in Jelastic

In such a way, the retrieved information can be used for establishment of internal connection to your Docker containers at Jelastic.

External Connection

In order to access your Docker container from outside of a Platform, i.e. from the Internet, Jelastic offers the following solutions:

1. If your service or application, that is running within Docker container, listens to the 80th port, then it will be automatically exposed to external network (over the assigned domain name) via Jelastic Shared Load Balancer.Open in Browser Jelastic

In such a case, you just need to click Open in browser for the corresponding node to launch it (this option works for HTTP connections).

Note: In case your Docker container does not have an external IP attached, Jelastic performs an automatic port redirect. This means that if application listens to a custom port on TCP level, Jelastic will try to automatically detect it and forward all the incoming requests to this port number. As a result, in most cases, your dockerized app or service will become available over the Internet under the corresponding node’s domain right after creation.
However, in case you’d like to prohibit such a possibility, you may declare the corresponding rules within your container’s firewall settings.

2. For more complex implementations, Jelastic provides special endpoints functionality (available within the same-named section of any environment’s Settings):Docker endpoints in Jelastic

It allows to expose the required private port on your container through the randomly chosen public port at Jelastic Shared Load Balancer, so it can be accessed via the provided Access URL.

3. And the last option, which gives the most freedom (allowing, for example, to secure your connection with Custom SSL, get rid of limitation on the simultaneous connections amount, etc) is attachment of Public IP address to your Docker container.Jelastic Public IP address

With it, your app can be configured to listen to any port you need and, in such a way, to become accessible via the external network.

While enabling the public IP option, please pay attention that it’s a paid add-on (the exact cost for its usage can be seen upon hovering over the price widget at the right part of your topology wizard or through navigating to Quotas & Pricing > Pricing > Options tab).

That’s all for now! Feel free to leverage the most suitable connection option among the described ones while working with your Docker containers. And as usual, we’re always glad to provide you with any required technical assistance at Stackoverflow in case you have some questions left.

Still don’t have an account? Register for free at any of our partners’ platforms within Jelastic Cloud Union and experience all of the advantages the Jelastic Dockers hosting provides by yourself!