How to handle the postgres connection when heroku changes the DATABASE_URL

Question

The value of your app’s DATABASE_URL config var might change at any time. You should not rely on this value either inside or outside your Heroku app.

I'm developing a Node.js server that uses node-postgres to connect and manage the connection pool with the database.

But what happens when Heroku changes the DATABASE_URL? How should this problem be managed?

Chris · Accepted Answer · 2019-04-12 14:03:38Z

3

You handle this by always connecting to Postgres using whatever value DATABASE_URL has. For example, you can use this value as a connection string when you create your pool:

const connectionString = process.env.DATABASE_URL

const pool = new Pool({
  connectionString: connectionString,
})

Heroku's dynos restart when their environment variables or addons are changed, which should cause your code to pick up the new database connection string when it starts back up.

edited Apr 12, 2019 at 14:03

answered Apr 12, 2019 at 13:36

Chris

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4 Comments

Phocs Over a year ago

I already use the environment variable. But some things are not clear to me: pool = new Pool ({connectionString: connectionString}) it is executed only the first time, after which, when a new connection is needed, it is searched among those already active and available, otherwise a new one is established. So the questions are immediate: 1) How does connectionString capture the change? 2) What happens to the connections already active in the Pool?

Chris Over a year ago

@alessiovolpe, when the variable changes your dyno should restart and pick up the new setting. I'll add that to my answer.

Phocs Over a year ago

Now I understand, otherwise I couldn't explain how the thing could be handled at run time. Thank you very much!

bendytree Over a year ago

If you have preboot enabled, heroku will not change the env and will not restart your dyno. Just confirmed this with Heroku support.

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