16 KiB
Replacing variables inside configs
Sometimes you have mods or plugins that require configuration information that is only available at runtime. For example if you need to configure a plugin to connect to a database, you don't want to include this information in your Git repository or Docker image. Or maybe you have some runtime information like the server name that needs to be set in your config files after the container starts.
For those cases there is the option to replace defined variables inside your configs with environment variables defined at container runtime.
When the environment variable REPLACE_ENV_IN_PLACE is set to true (the default), the startup script will go through all files inside the container's /data path and replace variables that match the container's environment variables. Variables can instead (or in addition to) be replaced in files sync'ed from /plugins, /mods, and /config by setting REPLACE_ENV_DURING_SYNC to true (defaults to false).
Variables that you want to replace need to be declared inside curly brackets and prefixed with a dollar sign, such as ${CFG_YOUR_VARIABLE}, which is same as many scripting languages.
You can also change REPLACE_ENV_VARIABLE_PREFIX, which defaults to "CFG_", to limit which environment variables are allowed to be used. For example, with "CFG_" as the prefix, the variable ${CFG_DB_HOST} would be subsituted, but not ${DB_HOST}.
If you want to use a file's content for value, such as when using secrets mounted as files, declare the placeholder named like normal in the file and declare an environment variable named the same but with the suffix _FILE.
For example, a my.cnf file could contain:
[client]
password = ${CFG_DB_PASSWORD}
...a secret declared in the compose file with:
secrets:
db_password:
external: true
...and finally the environment variable would be named with a _FILE suffix and point to the mounted secret:
environment:
CFG_DB_PASSWORD_FILE: /run/secrets/db_password
Variables will be replaced in files with the following extensions:
.yml, .yaml, .txt, .cfg, .conf, .properties.
Specific files can be excluded by listing their name (without path) in the variable REPLACE_ENV_VARIABLES_EXCLUDES.
Paths can be excluded by listing them in the variable REPLACE_ENV_VARIABLES_EXCLUDE_PATHS. Path
excludes are recursive. Here is an example:
REPLACE_ENV_VARIABLES_EXCLUDE_PATHS="/data/plugins/Essentials/userdata /data/plugins/MyPlugin"
Here is a full example where we want to replace values inside a database.yml.
---
database:
host: ${CFG_DB_HOST}
name: ${CFG_DB_NAME}
password: ${CFG_DB_PASSWORD}
This is how your docker-compose.yml file could look like:
version: "3.8"
# Other docker-compose examples in /examples
services:
minecraft:
image: itzg/minecraft-server
ports:
- "25565:25565"
volumes:
- "mc:/data"
environment:
EULA: "TRUE"
ENABLE_RCON: "true"
RCON_PASSWORD: "testing"
RCON_PORT: 28016
# enable env variable replacement
REPLACE_ENV_VARIABLES: "TRUE"
# define an optional prefix for your env variables you want to replace
ENV_VARIABLE_PREFIX: "CFG_"
# and here are the actual variables
CFG_DB_HOST: "http://localhost:3306"
CFG_DB_NAME: "minecraft"
CFG_DB_PASSWORD_FILE: "/run/secrets/db_password"
volumes:
mc:
rcon:
secrets:
db_password:
file: ./db_password
Patching existing files
JSON path based patches can be applied to one or more existing files by setting the variable PATCH_DEFINITIONS to the path of a directory that contains one or more patch definition json files or a patch set json file.
Variable placeholders in the patch values can be restricted by setting REPLACE_ENV_VARIABLE_PREFIX, which defaults to "CFG_".
The following example shows a patch-set file were various fields in the paper.yaml configuration file can be modified and added:
{
"patches": [
{
"file": "/data/paper.yml",
"ops": [
{
"$set": {
"path": "$.verbose",
"value": true
}
},
{
"$set": {
"path": "$.settings['velocity-support'].enabled",
"value": "${CFG_VELOCITY_ENABLED}",
"value-type": "bool"
}
},
{
"$put": {
"path": "$.settings",
"key": "my-test-setting",
"value": "testing"
}
}
]
}
]
}
NOTES: Only JSON and Yaml files can be patched at this time. TOML support is planned to be added next. Removal of comments and other cosmetic changes will occur when patched files are processed.
Running with a custom server JAR
If you would like to run a custom server JAR, set -e TYPE=CUSTOM and pass the custom server
JAR via CUSTOM_SERVER. It can either be a URL or a container path to an existing JAR file.
If it is a URL, it will only be downloaded into the /data directory if it wasn't already. As
such, if you need to upgrade or re-download the JAR, then you will need to stop the container,
remove the file from the container's /data directory, and start again.
Force re-download of the server file
For VANILLA, FORGE, BUKKIT, SPIGOT, PAPER, CURSEFORGE, SPONGEVANILLA server types, set
$FORCE_REDOWNLOAD to some value (e.g. 'true) to force a re-download of the server file for
the particular server type. by adding a -e FORCE_REDOWNLOAD=true to your command-line.
For example, with PaperSpigot, it would look something like this:
docker run -d -v /path/on/host:/data \
-e TYPE=PAPER -e FORCE_REDOWNLOAD=true \
-p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
Running as alternate user/group ID
By default, the container will switch to user ID 1000 and group ID 1000;
however, you can override those values by setting UID and/or GID as environmental entries, during the docker run command.
-e UID=1234
-e GID=1234
The container will also skip user switching if the --user/-u argument
is passed to docker run.
Memory Limit
By default, the image declares an initial and maximum Java memory-heap limit of 1 GB. There are several ways to adjust the memory settings:
MEMORY: "1G" by default, can be used to adjust both initial (Xms) and max (Xmx) memory heap settings of the JVMINIT_MEMORY: independently sets the initial heap sizeMAX_MEMORY: independently sets the max heap size
The values of all three are passed directly to the JVM and support format/units as <size>[g|G|m|M|k|K]. For example:
-e MEMORY=2G
To let the JVM calculate the heap size from the container declared memory limit, unset MEMORY with an empty value, such as -e MEMORY="". By default, the JVM will use 25% of the container memory limit as the heap limit; however, as an example the following would tell the JVM to use 75% of the container limit of 2GB of memory:
-e MEMORY="" -e JVM_XX_OPTS="-XX:MaxRAMPercentage=75" -m 2000M
The settings above only set the Java heap limits. Memory resource requests and limits on the overall container should also account for non-heap memory usage. An extra 25% is a general best practice.
JVM Options
General JVM options can be passed to the Minecraft Server invocation by passing a JVM_OPTS
environment variable. The JVM requires -XX options to precede -X options, so those can be declared in JVM_XX_OPTS. Both variables are space-delimited, raw JVM arguments.
docker run ... -e JVM_OPTS="-someJVMOption someJVMOptionValue" ...
NOTE When declaring JVM_OPTS in a compose file's environment section with list syntax, do not include the quotes:
environment:
- EULA=true
- JVM_OPTS=-someJVMOption someJVMOptionValue
Using object syntax is recommended and more intuitive:
environment:
EULA: "true"
JVM_OPTS: "-someJVMOption someJVMOptionValue"
# or
# JVM_OPTS: -someJVMOption someJVMOptionValue
As a shorthand for passing several system properties as -D arguments, you can instead pass a comma separated list of name=value or name:value pairs with JVM_DD_OPTS. (The colon syntax is provided for management platforms like Plesk that don't allow = inside a value.)
For example, instead of passing
JVM_OPTS: -Dfml.queryResult=confirm -Dname=value
you can use
JVM_DD_OPTS: fml.queryResult=confirm,name=value
Extra Arguments
Arguments that would usually be passed to the jar file (those which are written after the filename) can be passed via the EXTRA_ARGS environment variable.
See Custom worlds directory path for an example.
Interactive and Color Console
If you would like to docker attach to the Minecraft server console with color and interactive capabilities, then add
-e EXEC_DIRECTLY=true
NOTES
This feature doesn't work via rcon, so you will need to
docker attachto the container. Use the sequence Ctrl-P, Ctrl-Q to detach.This will bypass graceful server shutdown handling when using
docker stop, so be sure the server console'sstopcommand.Make to enable stdin and tty with
-itwhen usingdocker runorstdin_open: trueandtty: truewhen using docker compose.This feature is incompatible with Autopause and cannot be set when
ENABLE_AUTOPAUSE=true.
Server Shutdown Options
To allow time for players to finish what they're doing during a graceful server shutdown, set STOP_SERVER_ANNOUNCE_DELAY to a number of seconds to delay after an announcement is posted by the server.
NOTE be sure to adjust Docker's shutdown timeout accordingly, such as using the -t option on docker-compose down.
OpenJ9 Specific Options
The openj9 image tags include specific variables to simplify configuration:
-e TUNE_VIRTUALIZED=TRUE: enables the option to optimize for virtualized environments-e TUNE_NURSERY_SIZES=TRUE: configures nursery sizes where the initial size is 50% of theMAX_MEMORYand the max size is 80%.
Enabling rolling logs
By default the vanilla log file will grow without limit. The logger can be reconfigured to use a rolling log files strategy by using:
-e ENABLE_ROLLING_LOGS=true
NOTE this will interfere with interactive/color consoles as described in the section above
Timezone Configuration
You can configure the timezone to match yours by setting the TZ environment variable:
-e TZ=Europe/London
such as:
docker run -d -it -e TZ=Europe/London -p 25565:25565 --name mc itzg/minecraft-server
Or mounting /etc/timezone as readonly (not supported on Windows):
-v /etc/timezone:/etc/timezone:ro
such as:
docker run -d -it -v /etc/timezone:/etc/timezone:ro -p 25565:25565 --name mc itzg/minecraft-server
Enable Remote JMX for Profiling
To enable remote JMX, such as for profiling with VisualVM or JMC, add the environment variable ENABLE_JMX=true, set JMX_HOST to the IP/host running the Docker container, and add a port forwarding of TCP port 7091, such as:
-e ENABLE_JMX=true -e JMX_HOST=$HOSTNAME -p 7091:7091
Enable Aikar's Flags
Aikar has done some research into finding the optimal JVM flags for GC tuning, which becomes more important as more users are connected concurrently. The set of flags documented there can be added using
-e USE_AIKAR_FLAGS=true
When MEMORY is greater than or equal to 12G, then the Aikar flags will be adjusted according to the article.
HTTP Proxy
You may configure the use of an HTTP/HTTPS proxy by passing the proxy's URL via the PROXY
environment variable. In the example compose file it references
a companion squid proxy by setting the equivalent of
-e PROXY=proxy:3128
Using "noconsole" option
Some older versions (pre-1.14) of Spigot required --noconsole to be passed when detaching stdin, which can be done by setting -e CONSOLE=FALSE.
Explicitly disable GUI
Some older servers get confused and think that the GUI interface is enabled. You can explicitly
disable that by passing -e GUI=FALSE.
Stop Duration
When the container is signalled to stop, the Minecraft process wrapper will attempt to send a "stop" command via RCON or console and waits for the process to gracefully finish. By default it waits 60 seconds, but that duration can be configured by setting the environment variable STOP_DURATION to the number of seconds.
Setup only
If you are using a host-attached data directory, then you can have the image setup the Minecraft server files and stop prior to launching the server process by setting SETUP_ONLY to true.
Enable Flare Flags
To enable the JVM flags required to fully support the Flare profiling suite, set the following variable:
-e USE_FLARE_FLAGS=true
Flare is built-in to Pufferfish/Purpur, and is available in plugin form for other server types.
Enable support for optimized SIMD operations
To enable support for optimized SIMD operations, the JVM flag can be set with the following variable:
-e USE_SIMD_FLAGS=true
SIMD optimized operations are supported by Pufferfish and Purpur.
Enable timestamps in init logs
Before the container starts the Minecraft Server its output is prefixed with [init], such as
[init] Starting the Minecraft server...
To also include the timestamp with each log, set LOG_TIMESTAMP to "true". The log output will then look like:
[init] 2022-02-05 16:58:33+00:00 Starting the Minecraft server...
Auto-execute RCON commands
RCON commands can be configured to execute when the server starts, a client connects, or a client disconnects.
!!! note
When declaring several commands within a compose file environment variable, it's easiest to use YAML's `|-` [block style indicator](https://yaml-multiline.info/).
On Server Start:
RCON_CMDS_STARTUP: |-
gamerule doFireTick false
pregen start 200
On Client Connection:
RCON_CMDS_ON_CONNECT: |-
team join New @a[team=]
Note:
- On client connect we only know there was a connection, and not who connected. RCON commands will need to be used for that.
On Client Disconnect:
RCON_CMDS_ON_DISCONNECT: |-
gamerule doFireTick true
On First Client Connect
RCON_CMDS_FIRST_CONNECT: |-
pregen stop
On Last Client Disconnect
RCON_CMDS_LAST_DISCONNECT: |-
kill @e[type=minecraft:boat]
pregen start 200
Example of rules for new players
Uses team NEW and team OLD to track players on the server. So move player with no team to NEW, run a command, move them to team OLD. Reference Article
RCON_CMDS_STARTUP: |-
/pregen start 200
/gamerule doFireTick false
/team add New
/team add Old
RCON_CMDS_ON_CONNECT: |-
/team join New @a[team=]
/give @a[team=New] birch_boat
/team join Old @a[team=New]
RCON_CMDS_FIRST_CONNECT: |-
/pregen stop
RCON_CMDS_LAST_DISCONNECT: |-
/kill @e[type=minecraft:boat]
/pregen start 200