docker-gen is a file generator that renders templates using docker container meta-data.

It can be used to generate various kinds of files for:

• Centralized logging - fluentd, logstash or other centralized logging tools that tail the containers JSON log file or files within the container.
• Log Rotation - logrotate files to rotate container JSON log files
• Reverse Proxy Configs - nginx, haproxy, etc. reverse proxy configs to route requests from the host to containers
• Service Discovery - Scripts (python, bash, etc..) to register containers within etcd, hipache, etc..

There are three common ways to run docker-gen:

• on the host
• bundled in a container with another application
• separate standalone containers

Download the version you need, untar, and install to your PATH.

wget https://github.com/nginx-proxy/docker-gen/releases/download/0.16.0/docker-gen-linux-amd64-0.16.0.tar.gztar xvzf docker-gen-linux-amd64-0.16.0.tar.gz./docker-gen

Docker-gen can be bundled inside of a container along-side applications.

nginx-proxy/nginx-proxy trusted build is an example of running docker-gen within a container along-side nginx. jwilder/docker-register is an example of running docker-gen within a container to do service registration with etcd.

It can also be run as two separate containers using the nginx-proxy/docker-gen image, together with virtually any other image.

This is how you could run the official nginx image and have docker-gen generate a reverse proxy config in the same way that nginx-proxy works. You may want to do this to prevent having the docker socket bound to a publicly exposed container service.

Start nginx with a shared volume:

docker run -d -p 80:80 --name nginx -v /tmp/nginx:/etc/nginx/conf.d -t nginx

Fetch the template and start the docker-gen container with the shared volume:

mkdir -p /tmp/templates && cd /tmp/templatescurl -o nginx.tmpl https://raw.githubusercontent.com/nginx-proxy/docker-gen/main/templates/nginx.tmpldocker run -d --name nginx-gen --volumes-from nginx \ -v /var/run/docker.sock:/tmp/docker.sock:rw \ -v /tmp/templates:/etc/docker-gen/templates \ -t nginxproxy/docker-gen -notify-sighup nginx -watch -only-exposed /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf

Start a container, taking note of any Environment variables a container expects. See the top of a template for details.

docker run --env VIRTUAL_HOST='example.com' --env VIRTUAL_PORT=80 ...

$ docker-gen Usage: docker-gen [options] template [dest] Generate files from docker container meta-data Options: -config path config files with template directives. Config files will be merged if this option is specified multiple times. (default []) -container-filter key=value container filter for inclusion by docker-gen. You can pass this option multiple times to combine filters with AND. https://docs.docker.com/engine/reference/commandline/ps/#filter -endpoint string docker api endpoint (tcp|unix://..). Default unix:///var/run/docker.sock -event-filter key=value additional filter for event watched by docker-gen (e.g -event-filter event=connect -event-filter event=disconnect). You can pass this option multiple times to combine filters. By default docker-gen listen for container events start, stop, die and health_status. https://docs.docker.com/engine/reference/commandline/events/#filtering-events -include-stopped include stopped containers. Bypassed when providing a container status filter (-container-filter status=foo). -interval int notify command interval (secs) -keep-blank-lines keep blank lines in the output file -notify restart xyz run command after template is regenerated (e.g restart xyz) -notify-container container-ID send -notify-signal signal (defaults to 1 / HUP) to container. You can pass this option multiple times to notify multiple containers. -notify-filter key=value container filter for notification (e.g -notify-filter name=foo). You can pass this option multiple times to combine filters with AND. https://docs.docker.com/engine/reference/commandline/ps/#filter -notify-output log the output(stdout/stderr) of notify command -notify-sighup container-ID send HUP signal to container. Equivalent to 'docker kill -s HUP container-ID', or `-notify-container container-ID -notify-signal 1`. You can pass this option multiple times to send HUP to multiple containers. -notify-signal signal signal to send to the -notify-container and -notify-filter. -1 to call docker restart. Defaults to 1 aka. HUP. All available signals available on the dockerclient https://github.com/fsouza/go-dockerclient/blob/main/signal.go -only-exposed only include containers with exposed ports. Bypassed when using the exposed filter with (-container-filter exposed=foo). -only-published only include containers with published ports (implies -only-exposed). Bypassed when providing a container published filter (-container-filter published=foo). -tlscacert string path to TLS CA certificate file (default "~/.docker/ca.pem") -tlscert string path to TLS client certificate file (default "~/.docker/cert.pem") -tlskey string path to TLS client key file (default "~/.docker/key.pem") -tlsverify verify docker daemon's TLS certicate -version show version -wait string minimum and maximum durations to wait (e.g. "500ms:2s") before triggering generate -watch watch for container changes Arguments: template - path to a template to generate dest - path to write the template to. If not specfied, STDOUT is used Environment Variables: DOCKER_HOST - default value for -endpoint DOCKER_CERT_PATH - directory path containing key.pem, cert.pem and ca.pem DOCKER_TLS_VERIFY - enable client TLS verification DOCKER_CONTAINER_FILTERS - comma separated list of container filters for inclusion by docker-gen. Filters supplied through this variable are ignored if -container-filter is provided. 

If no <dest> file is specified, the output is sent to stdout. Mainly useful for debugging.

Using the -config flag from above you can tell docker-gen to use the specified config file instead of command-line options. Multiple templates can be defined and they will be executed in the order that they appear in the config file.

An example configuration file, docker-gen.cfg can be found in the examples folder.

[[config]] # Starts a configuration sectiondest = "path/to/a/file"# path to write the template. If not specfied, STDOUT is usednotifycmd = "/etc/init.d/foo reload"# run command after template is regenerated (e.g restart xyz)onlyexposed = true # only include containers with exposed portstemplate = "/path/to/a/template/file.tmpl"# path to a template to generatewatch = true # watch for container changeswait = "500ms:2s"# debounce changes with a min:max duration. Only applicable if watch = true[config.NotifyContainers]# Starts a notify container sectioncontainername = 1 # container name followed by the signal to sendcontainer_id = 1 # or the container id can be used followed by the signal to send

Putting it all together here is an example configuration file.

[[config]] template = "/etc/nginx/nginx.conf.tmpl"dest = "/etc/nginx/sites-available/default"onlyexposed = true notifycmd = "/etc/init.d/nginx reload"[[config]] template = "/etc/logrotate.conf.tmpl"dest = "/etc/logrotate.d/docker"watch = true [[config]] template = "/etc/docker-gen/templates/nginx.tmpl"dest = "/etc/nginx/conf.d/default.conf"watch = true wait = "500ms:2s"[config.NotifyContainers]nginx = 1 # 1 is a signal number to be sent; here SIGHUPe75a60548dc9 = 1 # a key can be either container name (nginx) or ID

The templates used by docker-gen are written using the Go text/template language. In addition to the built-in functions supplied by Go, docker-gen uses sprig and some additional functions to make it simpler (or possible) to generate your desired output. Some templates rely on environment variables within the container to make decisions on what to generate from the template.

Several templates may be parsed at once by using a semicolon (;) to delimit the template value. This can be used as a proxy for Golang's nested template functionality. In all cases, the main rendered template should go first.

[[config]] template = "/etc/docker-gen/templates/nginx.tmpl;/etc/docker-gen/templates/header.tmpl" dest = "/etc/nginx/conf.d/default.conf" watch = true wait = "500ms:2s" 

Within the templates, the object emitted by docker-gen will be a structure consisting of following Go structs:

typeRuntimeContainerstruct{IDstringCreated time.TimeAddresses []AddressNetworks []NetworkGatewaystringNamestringHostnamestringImageDockerImageEnvmap[string]stringVolumesmap[string]VolumeNodeSwarmNodeLabelsmap[string]stringIPstringIP6LinkLocalstringIP6GlobalstringMounts []MountStateState } typeAddressstruct{IPstringIP6LinkLocalstringIP6GlobalstringPortstringHostPortstringProtostringHostIPstring } typeNetworkstruct{IPstringNamestringGatewaystringEndpointIDstringIPv6GatewaystringGlobalIPv6AddressstringMacAddressstringGlobalIPv6PrefixLenintIPPrefixLenintInternalbool } typeDockerImagestruct{RegistrystringRepositorystringTagstring } typeMountstruct{NamestringSourcestringDestinationstringDriverstringModestringRWbool } typeVolumestruct{PathstringHostPathstringReadWritebool } typeSwarmNodestruct{IDstringNamestringAddressAddress } typeStatestruct{RunningboolHealthHealth } typeHealthstruct{Statusstring } // Accessible from the root in templates as .DockertypeDockerstruct{NamestringNumContainersintNumImagesintVersionstringApiVersionstringGoVersionstringOperatingSystemstringArchitecturestringCurrentContainerIDstring } // Host environment variables accessible from root in templates as .Env

For example, this is a JSON version of an emitted RuntimeContainer struct:

{"ID": "71e9768075836eb38557adcfc71a207386a0c597dbeda240cf905df79b18cebf", "Addresses": [{"IP": "172.17.0.4", "Port": "22", "Proto": "tcp", "HostIP": "192.168.10.24", "HostPort": "2222" } ], "Gateway": "172.17.42.1", "Node":{"ID": "I2VY:P7PF:TZD5:PGWB:QTI7:QDSP:C5UD:DYKR:XKKK:TRG2:M2BL:DFUN", "Name": "docker-test", "Address":{"IP": "192.168.10.24" } }, "Labels":{"operatingsystem": "Ubuntu 14.04.2 LTS", "storagedriver": "devicemapper", "anything_foo": "something_bar" }, "IP": "172.17.0.4", "Name": "docker_register", "Hostname": "71e976807583", "Image":{"Registry": "jwilder", "Repository": "docker-register" }, "Env":{"ETCD_HOST": "172.17.42.1:4001", "PATH": "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin", "DOCKER_HOST": "unix:///var/run/docker.sock", "HOST_IP": "172.17.42.1" }, "Volumes":{"/mnt":{"Path": "/mnt", "HostPath": "/Users/joebob/tmp", "ReadWrite": true } } }

• Functions from Go
• Functions from Sprig v3, except for those that have the same name as one of the following functions.
• closest $array $value: Returns the longest matching substring in $array that matches $value
• coalesce ...: Returns the first non-nil argument.
• comment $delimiter $string: Returns $string with each line prefixed by $delimiter (helpful for debugging combined with Sprig toPrettyJson: {{toPrettyJson $ | comment "#" }}).
• contains $map $key: Returns true if $map contains $key. Takes maps from string to any type.
• dir $path: Returns an array of filenames in the specified $path.
• exists $path: Returns true if $path refers to an existing file or directory. Takes a string.
• eval $templateName [$data]: Evaluates the named template like Go's built-in template action, but instead of writing out the result it returns the result as a string so that it can be post-processed. The $data argument may be omitted, which is equivalent to passing nil.
• groupBy $containers $fieldPath: Groups an array of RuntimeContainer instances based on the values of a field path expression $fieldPath. A field path expression is a dot-delimited list of map keys or struct member names specifying the path from container to a nested value, which must be a string. Returns a map from the value of the field path expression to an array of containers having that value. Containers that do not have a value for the field path in question are omitted.
• groupByWithDefault $containers $fieldPath $defaultValue: Returns the same as groupBy, but containers that do not have a value for the field path are instead included in the map under the $defaultValue key.
• groupByKeys $containers $fieldPath: Returns the same as groupBy but only returns the keys of the map.
• groupByMulti $containers $fieldPath $sep: Like groupBy, but the string value specified by $fieldPath is first split by $sep into a list of strings. A container whose $fieldPath value contains a list of strings will show up in the map output under each of those strings.
• groupByLabel $containers $label: Returns the same as groupBy but grouping by the given label's value. Containers that do not have the $label set are omitted.
• groupByLabelWithDefault $containers $label $defaultValue: Returns the same as groupBy but grouping by the given label's value. Containers that do not have the $label set are included in the map under the $defaultValue key.
• include $file: Returns content of $file, and empty string if file reading error.
• intersect $slice1 $slice2: Returns the strings that exist in both string slices.
• fromYaml $string / mustFromYaml $string: Similar to Sprig's fromJson / mustFromJson, but for YAML.
• toYaml $dict / mustToYaml $dict: Similar to Sprig's toJson / mustToJson, but for YAML.
• keys $map: Returns the keys from $map. If $map is nil, a nil is returned. If $map is not a map, an error will be thrown.
• sortStringsAsc $strings: Returns a slice of strings $strings sorted in ascending order.
• sortStringsDesc $strings: Returns a slice of strings $strings sorted in descending (reverse) order.
• sortObjectsByKeysAsc $objects $fieldPath: Returns the array $objects, sorted in ascending order based on the values of a field path expression $fieldPath.
• sortObjectsByKeysDesc $objects $fieldPath: Returns the array $objects, sorted in descending (reverse) order based on the values of a field path expression $fieldPath.
• when $condition $trueValue $falseValue: Returns the $trueValue when the $condition is true and the $falseValue otherwise
• where $items $fieldPath $value: Filters an array or slice based on the values of a field path expression $fieldPath. A field path expression is a dot-delimited list of map keys or struct member names specifying the path from container to a nested value. Returns an array of items having that value.
• whereNot $items $fieldPath $value: Filters an array or slice based on the values of a field path expression $fieldPath. A field path expression is a dot-delimited list of map keys or struct member names specifying the path from container to a nested value. Returns an array of items not having that value.
• whereExist $items $fieldPath: Like where, but returns only items where $fieldPath exists (is not nil).
• whereNotExist $items $fieldPath: Like where, but returns only items where $fieldPath does not exist (is nil).
• whereAny $items $fieldPath $sep $values: Like where, but the string value specified by $fieldPath is first split by $sep into a list of strings. The comparison value is a string slice with possible matches. Returns items which OR intersect these values.
• whereAll $items $fieldPath $sep $values: Like whereAny, except all $values must exist in the $fieldPath.
• whereLabelExists $containers $label: Filters a slice of containers based on the existence of the label $label.
• whereLabelDoesNotExist $containers $label: Filters a slice of containers based on the non-existence of the label $label.
• whereLabelValueMatches $containers $label $pattern: Filters a slice of containers based on the existence of the label $label with values matching the regular expression $pattern.

Sprig functions that have the same name as docker-gen function (but different behaviour) are made available with the sprig prefix:

• sprigCoalesce ...: Alias for Sprig's coalesce.
• sprigContains $string $string: Alias for Sprig's contains.
• sprigDir $path: Alias for Sprig's dir.
• sprigReplace $old $new $string: Alias for Sprig's replace.
• sprigSplit $sep $string: Alias for Sprig's split.
• sprigSplitn $sep $count $string": Alias for Sprig's splitn.

Some functions are aliases for Go's strings package functions:

• parseBool $string: Alias for strconv.ParseBool. Returns the boolean value represented by $string. It accepts 1, t, T, TRUE, true, True, 0, f, F, FALSE, false, False. Any other value returns an error.
• replace $string $old $new $count: Alias for strings.Replace. Replaces up to $count occurences of $old with $new in $string.
• split $string $sep: Alias for strings.Split. Splits $string into a slice of substrings delimited by $sep.
• splitN $string $sep $count: Alias for strings.SplitN. Splits $string into a slice of substrings delimited by $sep, with number of substrings returned determined by $count.
• toLower $string: Alias for strings.ToLower. Replace capital letters in $string to lowercase.
• toUpper $string: Alias for strings.ToUpper. Replace lowercase letters in $string to uppercase.

Those have been aliased to Sprig functions with the same behaviour as the original docker-gen function:

• json $value: Alias for Sprig's mustToJson
• parseJson $string: Alias for Sprig's mustFromJson.
• sha1 $string: Alias for Sprig's sha1sum.

• Automated Nginx Reverse Proxy for Docker
• Docker Log Management With Fluentd
• Docker Service Discovery Using Etcd and Haproxy

nginxproxy/nginx-proxy trusted build.

Start nginx-proxy:

docker run -d -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock -t nginxproxy/nginx-proxy

Then start containers with a VIRTUAL_HOST (and the VIRTUAL_PORT if more than one port is exposed) env variable:

docker run -e VIRTUAL_HOST=foo.bar.com -e VIRTUAL_PORT=80 -t ...

If you wanted to run docker-gen directly on the host, you could do it with:

docker-gen -only-published -watch -notify "/etc/init.d/nginx reload" templates/nginx.tmpl /etc/nginx/sites-enabled/default

This template generate a fluentd.conf file used by fluentd. It would then ship log files off the host.

docker-gen -watch -notify "restart fluentd" templates/fluentd.tmpl /etc/fluent/fluent.conf

This template is an example of generating a script that is then executed. This template generates a python script that is then executed which register containers in Etcd using its HTTP API.

docker-gen -notify "/bin/bash /tmp/etcd.sh" -interval 10 templates/etcd.tmpl /tmp/etcd.sh

This project uses Go Modules for managing 3rd party dependencies. This means that at least go 1.11 is required.

For go 1.11 and go 1.12 it is additionally required to manually enable support by setting GO111MODULE=on. For later versions, this is not required.

git clone <your fork>cd <your fork>make get-depsmake