Configuration

dyndo-server is configured by layering three sources, each overriding the one before it:

built-in defaults,
a config.yaml file, then
DYNDO_-prefixed environment variables.

There are no command-line flags. Configuration is deserialized directly into OpenDAL’s backend config structs, so backend settings are exactly OpenDAL’s own.

Configuration file

The file is ./config.yaml in the working directory by default. Set DYNDO_CONFIG to load a different path:

Variable	Description
`DYNDO_CONFIG`	Path to the YAML config file. If set, the file must exist or the server exits. If unset, a missing `config.yaml` is ignored (defaults + env are used).

Schema

Key	Type	Description	Default
`store`	`fs` \| `s3`	Which storage backend serves assets.	`fs`
`server.host`	string	Listen address.	`0.0.0.0`
`server.port`	integer	Listen port.	`8080`
`fs`	table	Local-filesystem backend settings (OpenDAL `Fs`). Required when `store: fs`.	(none)
`s3`	table	S3 backend settings (OpenDAL `S3`). Required when `store: s3`.	(none)

Neither backend section is defaulted: whichever backend store selects must be supplied (via file or environment) with the fields OpenDAL needs, or the server fails to build its storage operator at startup.

`fs` backend

Key	Description
`fs.root`	Root directory that descriptors and media are read from. Required for `store: fs`.

store: fs
fs:
  root: ./assets

`s3` backend

The s3 table is OpenDAL’s S3 configuration. The commonly used keys:

Key	Description
`s3.bucket`	Bucket name. Required for `store: s3`.
`s3.region`	AWS region.
`s3.endpoint`	Service endpoint URL.
`s3.root`	Key prefix prepended to every object path.
`s3.access_key_id`	Access key ID (or supply via `AWS_ACCESS_KEY_ID`).
`s3.secret_access_key`	Secret access key (or supply via `AWS_SECRET_ACCESS_KEY`).

store: s3
s3:
  bucket: my-assets
  region: eu-west-1
  endpoint: https://s3.eu-west-1.amazonaws.com
  root: /

Credentials may be omitted from the file and supplied through the standard AWS_* environment variables, which OpenDAL’s S3 backend reads.

Environment variables

Every setting maps to a DYNDO_-prefixed variable. Nested keys are separated by a double underscore (__); single underscores within a field name are preserved.

Variable	Sets
`DYNDO_STORE`	`store`
`DYNDO_SERVER__HOST`	`server.host`
`DYNDO_SERVER__PORT`	`server.port`
`DYNDO_FS__ROOT`	`fs.root`
`DYNDO_S3__BUCKET`	`s3.bucket`
`DYNDO_S3__REGION`	`s3.region`
`DYNDO_S3__ACCESS_KEY_ID`	`s3.access_key_id`
`DYNDO_S3__SECRET_ACCESS_KEY`	`s3.secret_access_key`

The double-underscore rule is what keeps a name like access_key_id intact — DYNDO_S3__ACCESS_KEY_ID nests as s3.access_key_id, not s3.access.key.id.

Precedence

Later layers win field by field (a deep merge), so you can commit a config.yaml and override only what changes per environment:

# config.yaml sets port 8080 and fs.root ./assets;
# these env vars override just those two fields.
DYNDO_SERVER__PORT=9000 DYNDO_FS__ROOT=/srv/media dyndo-server

Startup errors

Configuration problems are reported at startup, not per request:

Condition	Result
`DYNDO_CONFIG` names a missing file	Exit: “DYNDO_CONFIG points to a missing file”.
YAML/env cannot be merged or deserialized into the schema	Exit: “failed to load configuration”.
Selected backend rejected (e.g. `s3` with no `bucket`, `fs` with no `root`)	Exit: “failed to build storage operator”.

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