Implement configstore maintenance mode and export/import.
When configstore is set in maintenance mode it'll start only the maintenance and
export/import handlers.
Setting maintenance mode will set a key in etcd so all the configstore instances
will detect it and enter in maintenance mode. This is done asyncronously so it
could take some time (future improvements will add some api to show all the
configstore states)
Export is always available and will export the datamanager contents.
Import is available only during maintenance, given a datamanager export will
import it and reset etcd to this import state.
Use the go sql context functions (ExecContext, QueryContext etc...)
The context is saved inside Tx so the library users should only pass it one time
to the db.Do function.
ErrInternal is an internal error that should be provided to the user (http api
will return a 500 with the error message)
It'll be used for any kind of error that are not auth or bad requests (like
errors to communicate to another service)
Don't create an ErrFromRemote wrapping the returned error but
wrap the ErrFromRemote
Also use xerrors Is/As to get the underlying error to return to api clients
while maintaining context for logging
Just a raw replace of "github.com/pkg/errors".
Next steps will improve errors (like remote errors, api errors, not exist errors
etc...) to leverage its functionalities
* client: always parse the json error message field and return its contents
* Use ErrBadRequest and ErrNotFound in every handler and command
* Gateway: by default pass underlying service error (configstore, runservice) to
client keeping the status code and message. In future, if some errors must be
masked, we should change the specific parts that need special handling.
* Always return a json message also on error. For internal errors return a
generic "internal server error" message to not leak the real internal error to
clients
* Return 201 Created on resource creation
* Return 204 No Content on resource deletion and other action with no json
output
Simone Gotti