Running Applications with Docker Compose and Troubleshooting Connection Issues

Before you apply changes made to a Compose configuration file, there is an opportunity to validate the content of the configuration file with the following command: ```console $ docker compose config ``` When this command is run, Docker Compose reads the file `compose.yaml`, parses it into a data structure in memory, validates where possible, and prints back the reconstruction of that configuration file from its internal representation. If this isn't possible due to errors, Docker prints an error message instead. ### Build and run the application using Docker Compose Start your application and confirm that it's running. ```console $ docker compose up --build ``` You passed the `--build` flag so Docker will compile your image and then start it. > [!NOTE] > > Docker Compose is a useful tool, but it has its own quirks. For example, no rebuild is triggered on the update to the source code unless the `--build` flag is provided. It is a very common pitfall to edit one's source code, and forget to use the `--build` flag when running `docker compose up`. Since your set-up is now run by Docker Compose, it has assigned it a project name, so you get a new volume for your CockroachDB instance. This means that your application will fail to connect to the database, because the database doesn't exist in this new volume. The terminal displays an authentication error for the database: ```text # ... omitted output ... rest-server | 2021/05/10 00:54:25 failed to initialise the store: pq: password authentication failed for user totoro roach | * roach | * INFO: Replication was disabled for this cluster. roach | * When/if adding nodes in the future, update zone configurations to increase the replication factor. roach | * roach | CockroachDB node starting at 2021-05-10 00:54:26.398177 +0000 UTC (took 3.0s) roach | build: CCL v20.1.15 @ 2021/04/26 16:11:58 (go1.13.9) roach | webui: http://db:8080 roach | sql: postgresql://root@db:26257?sslmode=disable roach | RPC client flags: /cockroach/cockroach <client cmd> --host=db:26257 --insecure roach | logs: /cockroach/cockroach-data/logs roach | temp dir: /cockroach/cockroach-data/cockroach-temp349434348 roach | external I/O path: /cockroach/cockroach-data/extern roach | store[0]: path=/cockroach/cockroach-data roach | storage engine: rocksdb roach | status: initialized new cluster roach | clusterID: b7b1cb93-558f-4058-b77e-8a4ddb329a88 roach | nodeID: 1 rest-server exited with code 0 rest-server | 2021/05/10 00:54:25 failed to initialise the store: pq: password authentication failed for user totoro rest-server | 2021/05/10 00:54:26 failed to initialise the store: pq: password authentication failed for user totoro rest-server | 2021/05/10 00:54:29 failed to initialise the store: pq: password authentication failed for user totoro rest-server | 2021/05/10 00:54:25 failed to initialise the store: pq: password authentication failed for user totoro rest-server | 2021/05/10 00:54:26 failed to initialise the store: pq: password authentication failed for user totoro rest-server | 2021/05/10 00:54:29 failed to initialise the store: pq: password authentication failed for user totoro rest-server exited with code 1 # ... omitted output ... ``` Because of the way you set up your deployment using `restart_policy`, the failing container is being restarted every 20 seconds. So, in order to fix the problem, you need to log in to the database engine and create the user. You've done it before in [Configure the database engine](#configure-the-database-engine).

This section discusses running applications with Docker Compose, including validating the configuration and using the `--build` flag during the `docker compose up` command. It also addresses a common issue where Docker Compose creates a new volume, leading to connection failures due to a missing database. The section provides an example of an authentication error and suggests logging into the database engine to create the user as a solution.