Externally Sourced Configuration File Values for Self-Managed Deployments
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MongoDB supports using expansion directives in configuration files to load externally sourced values. Expansion directives can load values for specific configuration file options or load the entire configuration file. Expansion directives help obscure confidential information like security certificates and passwords.
storage: dbPath: "/var/lib/mongo" systemLog: destination: file path: "/var/log/mongodb/mongod.log" net: bindIp: __exec: "python /home/user/getIPAddresses.py" type: "string" trim: "whitespace" digest: 85fed8997aac3f558e779625f2e51b4d142dff11184308dc6aca06cff26ee9ad digest_key: 68656c6c30303030307365637265746d796f6c64667269656e64 tls: mode: requireTLS certificateKeyFile: "/etc/tls/mongod.pem" certificateKeyFilePassword: __rest: "https://myrestserver.example.net/api/config/myCertKeyFilePassword" type: "string" digest: b08519162ba332985ac18204851949611ef73835ec99067b85723e10113f5c26 digest_key: 6d795365637265744b65795374756666
If the configuration file includes the
__rest
expansion, on Linux/macOS, the read access to the configuration file must be limited to the user running themongod
/mongos
process only.If the configuration file includes the
__exec
expansion, on Linux/macOS, the write access to the configuration file must be limited to the user running themongod
/mongos
process only.
To use expansion directives, you must specify the
--configExpand
command-line option
with the complete list of expansion directives used:
mongod --config "/path/to/config/mongod.conf" --configExpand "rest,exec"
If you omit the
--configExpand
option or if
you do not specify the complete list of expansion directives used in
the configuration file, the mongod
/mongos
returns
an error and terminates. You can only specify the
--configExpand
option on the
command line.
Use the __rest
Expansion Directive
The __rest
expansion directive loads configuration
file values from a REST
endpoint. __rest
supports loading
specific values in the configuration file or loading the entire
configuration file.
The following configuration file uses the
__rest
expansion directive to load the
setting net.tls.certificateKeyFilePassword
value from an
external REST
endpoint:
storage: dbPath: "/var/lib/mongo" systemLog: destination: file path: "/var/log/mongodb/mongod.log" net: bindIp: 192.51.100.24,127.0.0.1 tls: mode: requireTLS certificateKeyFile: "/etc/tls/mongod.pem" certificateKeyFilePassword: __rest: "https://myrestserver.example.net/api/config/myCertKeyFilePassword" type: "string"
- File Permission
- If the configuration file includes the
__rest
expansion, on Linux/macOS, the read access to the configuration file must be limited to the user running themongod
/mongos
process only. - Expansion Parsing
To parse the
__rest
blocks, start themongod
/mongos
with the--configExpand "rest"
option.The
mongod
/mongos
issues aGET
request against specified URL. If successful, themongod
/mongos
replaces the value ofcertificateKeyFilePassword
with the returned value. If the URL fails to resolve or if theREST
endpoint returns an invalid value, themongod
/mongos
throws an error and terminates.
The following configuration file uses the
__rest
expansion directive to load the
configuration file from an external REST
endpoint. The
expansion directive and its options must be the only values
specified in the configuration file.
__rest: "https://myrestserver.example.net/api/config/fullConfig" type: "yaml"
- File Permission
- If the configuration file includes the
__rest
expansion, on Linux/macOS, the read access to the configuration file must be limited to the user running themongod
/mongos
process only. - Expansion Parsing
To parse the
__rest
blocks, start themongod
/mongos
with the--configExpand "rest"
option.The
mongod
/mongos
issues aGET
request against the specified URL. If successful, themongod
/mongos
parses the returned configurationyaml
file and uses it during startup. If the URL fails to resolve or return a properly formattedyaml
file, themongod
/mongos
throws an error and terminates.
Use the __exec
Expansion Directive
The __exec
expansion directive loads configuration
file values from a shell or terminal command. __exec
supports
loading specific values in the configuration file or loading the
entire configuration file.
The following example configuration file uses the
__exec
expansion directive to to load the
setting net.tls.certificateKeyFilePassword
value from the output
of a shell or terminal command:
storage: dbPath: "/var/lib/mongo" systemLog: destination: file path: "/var/log/mongodb/mongod.log" net: bindIp: 192.51.100.24,127.0.0.1 tls: mode: requireTLS certificateKeyFile: "/etc/tls/mongod.pem" certificateKeyFilePassword: __exec: "python /home/myUserName/getPEMPassword.py" type: "string"
- File Permission
- If the configuration file includes the
__exec
expansion, on Linux/macOS, the write access to the configuration file must be limited to the user running themongod
/mongos
process only. - Expansion Parsing
To parse the
__exec
blocks, start themongod
/mongos
with the--configExpand "exec"
option.The
mongod
/mongos
attempts to execute the specified operation. If the command executes successfully, themongod
/mongos
replaces the value ofcertificateKeyFilePassword
with the returned value. If the command fails or returns an invalid value for the configuration file setting, themongod
/mongos
throws an error and terminates.
The following example configuration file uses the
__exec
expansion directive to load the
configuration file from the output of a shell or terminal
command. The __exec
expansion directive
and its options must be the only values specified in the
configuration file.
__exec: "python /home/myUserName/getFullConfig.py" type: "yaml"
- File Permission
- If the configuration file includes the
__exec
expansion, on Linux/macOS, the write access to the configuration file must be limited to the user running themongod
/mongos
process only. - Expansion Parsing
To parse the
__exec
blocks, start themongod
/mongos
with the--configExpand "rest"
option.If the command executes successfully, the
mongod
/mongos
parses the returned configurationyaml
file and uses it during startup. If the command fails or returns an invalidyaml
file, themongod
/mongos
throws an error and terminates.
Expansion Directives Reference
__rest
The
__rest
expansion directive loads configuration file values from aREST
endpoint.__rest
supports loading specific values in the configuration file or loading the entire configuration file. Themongod
/mongos
then starts using the externally sourced values as part of its configuration.The
__rest
expansion directive has the following syntax:To specify a
REST
endpoint for a specific configuration file setting or settings:<some configuration file setting>: __rest: "<string>" type: "string" trim: "none|whitespace" digest: "<string>" digest_key: "<string>" To specify a
REST
endpoint for the entire configuration file:__rest: "<string>" type: "yaml" trim: "none|whitespace" If specifying the entire configuration file via
REST
endpoint, the expansion directive and its options must be the only values specified in the configuration file.
__rest
takes the following fields:FieldTypeDescriptionstringRequired The URL against which the
mongod
/mongos
issues aGET
request to retrieve the externally sourced value.For non-localhost
REST
endpoints (e.g. aREST
endpoint hosted on a remote server),__rest
requires encrypted (https://
) URLs where both the host machine and the remote server support TLS 1.1 or later.If the
REST
endpoint specified in the URL requires authentication, encode credentials into the URL with the standard RFC 3986 User Information format.For localhost
REST
endpoints (e.g. aREST
endpoint listening on the host machine),__rest
allows unencrypted (http://
) URLs.type
stringOptional Controls how
__rest
parses the returned value from the specified URL.Possible values are:
string
(Default)Directs
__rest
to parse the returned data as a literal string. If specifyingstring
, the entire__rest
block and supporting options must be nested under the field for which you are loading externally sourced values.yaml
Directs
__rest
to parse the returned data as ayaml
formatted file. If specifyingyaml
, the__rest
block must be the only content in the configuration file. Themongod
/mongos
replaces the configuration file contents with theyaml
retrieved from the REST resource.
trim
stringOptional Specifywhitespace
to direct__rest
to trim any leading or trailing whitespace, specifically occurrences of" "
,"\r"
,"\n"
,"\t"
,"\v"
, and"\f"
. Defaults tonone
, or no trimming.stringOptional. The SHA-256 digest of the expansion result.
If specified, you must also specify the digest_key.
stringNote
For examples, see Use the
__rest
Expansion Directive.
__exec
The
__exec
expansion directive loads configuration file values from the output of a shell or terminal command.__exec
supports loading specific values in the configuration file or loading the entire configuration file. Themongod
/mongos
then starts using the externally sourced values as part of its configuration.The
__exec
expansion directive has the following syntax:To specify a shell or terminal command for a specific configuration file setting or settings:
<some configuration file setting>: __exec: "<string>" type: "string" trim: "none|whitespace" To specify a a shell or terminal command for the entire configuration file:
__exec: "<string>" type: "yaml" trim: "none|whitespace" If specifying the entire configuration file via a terminal or shell command, the expansion directive and its options must be the only values specified in the configuration file.
__exec
takes the following fields:FieldTypeDescription__exec
stringRequired The string which the
mongod
/mongos
executes on the terminal or shell to retrieve the externally sourced value.On Linux and OSX hosts, execution is handled via POSIX
popen()
. On Windows hosts, execution is handled via the process control API.__exec
opens a read-only pipe as the same user that started themongod
ormongos
.type
stringOptional Controls how
__exec
parses the value returned by the executed command.Possible values are:
string
(Default )Directs
__exec
to parse the returned data as a literal string. If specifyingstring
, the entire__exec
block and supporting options must be nested under the field for which you are loading externally sourced values.yaml
Directs
__exec
to parse the returned data as ayaml
formatted file. If specifyingyaml
, the__exec
block must be the only content in the configuration file. Themongod
/mongos
replaces the configuration file contents with theyaml
retrieved from the executed command.
trim
stringOptional Specifywhitespace
to direct__exec
to trim any leading or trailing whitespace, specifically occurrences of" "
,"\r"
,"\n"
,"\t"
,"\v"
, and"\f"
. Defaults tonone
, or no trimming.stringOptional. The SHA-256 digest of the expansion result.
If specified, you must also specify the digest_key
stringNote
If the configuration file includes the
__exec
expansion, on Linux/macOS, the write access to the configuration file must be limited to the user running themongod
/mongos
process only.To enable parsing of the
__exec
expansion directives, start themongod
/mongos
with the--configExpand "exec"
option.
For examples, see Use the
__exec
Expansion Directive.
Output the Configuration File with Resolved Expansion Directive Values
You can test the final output of a configuration file that specifies one
or more expansion directives by starting the mongod
/mongos
with the
--outputConfig
option. A mongod
/mongos
started with --outputConfig
outputs
the resolved YAML configuration document to stdout
and halts. If any
expansion directive specified in the configuration file returns
additional expansion directives, the mongod
/mongos
throws an error and
terminates.
Warning
The --outputConfig
option returns
the resolved values for any field using an expansion directive. This
includes any private or sensitive information previously obscured by
using an external source for the configuration option.
For example, the following configuration file
mongod.conf
contains a __rest
expansion
directive:
storage: dbPath: "/var/lib/mongo" systemLog: destination: file path: "/var/log/mongodb/mongod.log" net: port: __rest: "https://mongoconf.example.net:8080/record/1" type: string
The string recorded at the specified URL is 20128
If the configuration file includes the __rest
expansion, on Linux/macOS, the read access to the configuration file must be limited
to the user running the mongod
/ mongos
process only.
Start the mongod
with the
--configExpand "rest"
and
--outputConfig
options:
mongod -f mongod.conf --configExpand rest --outputConfig
The mongod
outputs the following to stdout
before terminating:
config: mongod.conf storage: dbPath: "/var/lib/mongo" systemLog: destination: file path: "/var/log/mongodb/mongod.log" net: port: 20128 outputConfig: true