Configure a container

Select a container in your App Space to open its settings: Overview, Resources, Env Vars, Volumes, Networks, Ports and Status.

Changes need a stop and a start

A setting you save is stored at once, but the running container keeps its old values until it is stopped and started again. This is true for environment variables, volumes and limits.

• Right after you save, an Apply changes button appears on the container. It does the stop and the start for you.
• If you have left the page since, select Stop and then Start on the container.
• Restart is not enough. A restart keeps the old values.

Caution

Starting one container starts the App Space again as a whole: the other containers are down for about half a minute too. Save all your changes first, then apply once.

Environment variables

On Env Vars, select Add variable and fill in Key and Value.

• Sensitive hides the value in the dashboard. Use it for passwords and keys.
• Description is a note for yourself. It is not passed to the container.

Then apply the change as described above. To check, open Terminal and print the variable:

echo "$DATABASE_URL"

Connect containers to each other

Containers in the same App Space reach each other by container name. An app that needs the database in the container named db connects to the host db:

postgres://app:password@db:5432/app

Other App Spaces cannot reach your containers, and a database needs no public address to be used by your app. Do not expose its port.

After adding a container, stop and start the App Space once

A container you add to an App Space that is already running cannot be found by name by the others yet. Select Stop and then Start on the App Space, and the name works.

Volumes

Without a volume, everything a container writes is lost when it is replaced. A database, or an app that stores uploads, needs one.

1. On the Containers tab, select Add volume.

2. Type a Name and a Size in whole GB. The dialog shows how much of the App Space’s disk is still free; all volumes together must fit in the plan’s disk.

3. Choose the container to attach it to, or attach it later from the container’s Volumes tab. The volume appears inside the container at the path you give, for example /var/lib/postgresql/data.

4. Apply the change.

• A volume keeps its data through stop, start, restart and a new build.
• A volume can be attached to more than one container.
• A volume cannot be made larger or deleted on its own yet. Choose its size with room to grow.
• Deleting the App Space deletes its volumes and their data.

CPU and memory limits

By default every container shares what the App Space’s plan has. On Resources you can give one container its own limit, so that a busy container cannot take everything.

• A limit is the most the container may use.
• A reservation is what it is guaranteed.
• The limits of all containers together cannot be more than the plan.

A container that uses more memory than it may is killed by the system. If that keeps happening, the App Space shows that the container keeps crashing: give it a higher limit, or use a larger plan.

See how much it uses

Status shows the container’s CPU, memory, traffic and disk use at this moment.