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xenvman is an extensible environment manager which is used to create environments for testing microservices.


xenvman can be used to:

  • Define environment templates using JavaScript
  • Create images on the fly
  • Spawn as many containers as needed inside an environment
  • Link containers together in a single isolated network
  • Expose container ports for external access
  • Dynamically change environment composition (add, stop, restart containers) on the fly

For a detailed example take a look at tutorial.


Please note, that even though xenvman binaries are provided for both Linux and MacOS, at the moment only Linux is officially supported.

Download release

Simply download the latest available binary for your OS/platform from here, rename the binary to xenvman and place anywhere in your $PATH.

Compilation from source

In order to compile xenvman from source you must have installed Golang with the minimum version of 1.11.

xenvman uses new feature introduced in Go version 1.11 - Modules and so you can clone the sources anywhere, no need to do it into $GOPATH.

The build process is super simple:

$ cd ~ && git clone && cd xenvman
$ make test && make build

If everything is good, there will be a xenvman executable in the project root, which you can copy anywhere in your $PATH and that would be it for the installation.


There are two ways to provide configuration: configuration file or environment variables.

Configuration file

xenvman uses toml as a configuration format. Most of the configuration parameters have reasonable default values so you can run the program even without supplying any configuration at all. An example file with all the available options can be found here.

In order to provide custom configuration, create a xenvman.toml file anywhere you like and run the server with -c option:

xenvman run -c <path-to-xenvman.toml>


Configuration parameters can also be provided using environment variables. The variable must be a capitalized version of config param with a special XENVMAN_ prefix.

For example, setting server listen address port can be done using these both ways:

listen = ":9876" using configuration file, or

XENVMAN_LISTEN=":9876" - using env.

Please note: use underscore (_) to separate nested fields when using env, not dots.

api_auth (XENVMAN_API_AUTH) [""]

Type of authentication backend to use. Available types include:

  • basic - HTTP basic auth

auth_basic [""]

Section specifying mapping from usernames to passwords for http basic auth.

container_engine (XENVMAN_CONTAINER_ENGINE) ["docker"]

Type of container engine to use. Currently only docker is supported.

export_address (XENVMAN_EXPORT_ADDRESS) ["localhost"]

The external address to expose to clients.

keepalive (XENVMAN_KEEPALIVE) ["2m"]

Default environment keepalive

listen (XENVMAN_LISTEN) [":9876"]

IP:port to listen on. If IP is ommitted, localhost will be used.

ports_range (XENVMAN_PORTS_RANGE) [[20000, 30000]]

A port range from which to take exposed ports, specified as a list of two [min, max] numbers.

tpl.base_dir (XENVMAN_TPL_BASE_DIR) [""]

Base directory where to search for templates.

tpl.ws_dir (XENVMAN_TPL_WS_DIR) [""]

Base directory where temporary image workspaces will be created.

tpl.mount_dir (XENVMAN_TPL_MOUNT_DIR) [""]

Base directory where temporary container mount dirs will be created.

tls.cert (XENVMAN_TLS_CERT) [""]

Path to TLS certificate file. If not set, TLS mode will not be used.

tls.key (XENVMAN_TLS_key) [""]

Path to TLS privatet key file. If not set, TLS mode will not be used.

Running API server

Running xenvman server is very simple:

  1. When using configuration file: xenvman run -c <path-to-xenvman.toml>
  2. When using env variables: XENVMAN_<PARAM>=<VALUE> xenvman run


Environment is an isolated bubble where one or more containers can be run together in order to provide a necessary playground for integration testing.

Environments are created, managed and destroyed using HTTP API provided by running xenvman server.

Please note: here environment is NOT the usual shell one.


An environment is set up by executing one or more templates, where a template is a a small program written in JavaScript which defines what images to build/fetch, what and how many containers to spawn, what files to mount inside containers, what ports to expose etc.

A template script is run by embedded JS interpreter inside xenvman server. One template is just one javascript file located within a template base directory (defined by tpl.base-dir configuration parameter, or XENVMAN_TPL.BASE_DIR environment variable).

A template file name must follow the format: <name>.tpl.js and can be located either directly within tpl base dir or in any sub-directory.

A fully qualified template name consists of javascript file name without .tpl.js suffix, preceeded by directory names relative to template base dir.

To make it clear, let's consider a simple example. Let's say our base dir is /opt/xenvman/base and it looks like this:


So here we have three templates with fully qualified names: db/mysql, db/mongo and custom.

Data directory

There's usually a bunch of files needed by template like Dockerfile to build images on the fly, configuration templates, required modules, shared libraries etc. All those files must be placed in a special directory called template data directory (or just data dir for short). Data dir must be located inside the same dir where template file is and must be named using the following format: <name>, where <name> is the same template name as in main json file.

Template javascript API provides functions to copy files from data dir to image workspace, mount them inside containers etc.

Please note, that all files in data directory are never changed by a template, they are always copied when needed.

Workspace directory

Because xenvman allows you to build docker images on the fly, there are often files you'd want to include in the image. All those files are collected in a special temporary dir called workspace. A workspace is a temporary directory, separately created for any image your template is trying to build during template execution. The only required file is a Dockerfile itself, which describes what kind of image you're building.

Mount directory

A mount directory is a temporary dir created for every container the template wants to run and holds files which will be mounted inside the container. You can create files in a mount dir by either copying them from a data dir (using container JS API) or by using data from template runtime parameters.

Template directories summary

The following picture provides a general view of template directories and their relations.

Template directories

Javascript API

As mentioned above, a template is a JavaScript program which uses special API to configure required environment. Let's take a closer look at template shape and form.

Please note: xenvman uses an embedded JS interpreter, which implies certain limitations as compared to running JS in a browser or in node.js ecosystem:

  • No DOM-related functions
  • "use strict" will parse, but does nothing
  • The regular expression engine (re2/regexp) is not fully compatible with the ECMA5 specification
  • Only ES5 is supported. ES6 features (eg: Typed Arrays) are not available

Template format

A template must define an entry point function:

function execute(tpl, params) {}

This function is expected to provide necessary instructions in order to configure an environment.

First parameter, tpl, is a template instance, while params is an arbitrary key-value object which is used to configure template by the caller.

Please note: calling tpl instance functions, such as BuildImage, FetchImage etc. does not cause these actions to occur immediately, instead they are scheduled and performed at later stages, after JS execution phase.

Template API

Template instance, which is passed as a first argument has the following methods:

BuildImage(name :: string) -> BuildImage

Instucts xenvman to build a new image with the given name. name parameter is the resulting Docker image name.

Return value is a BuildImage instance.

FetchImage(name :: string) -> FetchImage

Instructs xenvman to fetch an existing image from public or private image repository.

The name is a fully-qualified docker image name, including repository address and tag, that is the same format is expected as for regular docker pull invocation.

For private repos, existing credentials (acquired by docker login) are used by the user who started xenvman server.

AddReadinessCheck(name :: string, params :: object) -> null

Adds a new readiness check for the current template.

BuildImage API

BuildImage instance represents an image which xenvman is going to build on the fly. Files included in the image can be either copied from a template data dir or by supplying data for files in template HTTP parameters.

CopyDataToWorkspace(path :: string...) -> null

This function takes a variable list of FS object names from data dir and copies them into image workspace. Object names must be relative to the data dir. For example, if data dir contained the following files:


then the paths would be: subdir/subfile.png and file1.json.

A special value * can be provided in order to copy every object from data dir.

AddFileToWorkspace(path :: string, data :: string, mode int) -> null

Sometimes you want to dynamically include some file into the image which is different every time you build it. So it cannot be simply placed into data dir. Imagine you've patched some microservice and want to test it, you can simply include the binary itself (assuming your microservice is written in a compiled language) in the HTTP request as a template parameter and by calling AddFileToWorkspace it will be copied to image workspace.

  • path argument is a path inside an image where to save the data.
  • data is the data itself as a binary/string. Usually it is base64-encoded during HTTP transfer and then decoded back using type.FromBase64() js function.
  • mode is a standard Unix file mode as an octal number.

InterpolateWorkspaceFile(file :: string, data :: object) -> null

Instructs xenvman to interpolate a file in a workspace dir (that is it must already be copied there before).

  • file is a file path relative to workspace dir.
  • data is an object providing values for interpolation.

More details about interpolation.

NewContainer(name :: string) -> Container

Create a new container with a given name from the image instance.

FetchImage API

FetchImage instance represents an image which will be fetched by xenvman (using Docker). Because in this case the image is already built the amount of possible actions is limited as compared to building a new image from scratch. Basically the only possible modification is mounting files into the container from the host (Mount dir).

NewContainer(name :: string) -> Container

Create a new container with a given name from the image instance.

Container API

SetEnv(env, val :: string) -> null

Sets a shell environment variable inside a container.

SetLabel(key :: string, value :: {string, number}) -> null

This function sets a container label. Labels here are xenvman entity and are used later during interpolation in order to filter containers.

SetCmd(cmd :: string...) -> null

Sets a CMD for the container.

SetEntrypoint(cmd :: string...) -> null

Sets an ENTRYPOINT for the container.

SetPorts(port :: number...) -> null

Instructs xenvman to expose certain ports from the container. Ports here are internal container ones, xenvman will select different external ports for every exposed one.

MountString(data, contFile :: string, mode :: int, opts :: object) -> null

Instructs xenvman to mount the data string into a container under the contFile name. mode is a regular Linux file mode expressed as an octal int. opts is an object, representing additional mounting parameters:

  • readonly :: bool - If mounted file should be read only.
  • interpolate :: bool - If the contents of a mounted file needs to be interpolated.
  • extra-interpolate-data :: object - Additional interpolation data. The data is accessible under .Extra key of a container instance inside templates.

MountData(dataFile, contFile :: string, opts :: object) -> null

Instructs xenvman to copy a dataFile from the [data dir](#Data directory) and mount it inside a container under contFile name.

In addition to opts from MountString above, MountData can take the following:

  • skip-if-nonexistent :: bool - If set to true, an error will not be raised if specified dataFile does not exist.

Readiness checks

xenvman was primarily designed to create environments for integration testing. Because of that, it needs to make sure an environment is ready before returning the access data to the caller. This is what readiness checks are for.

An environment can define any number of readiness checks and xenvman will only return back to the caller after all the checks for all the used templates are completed.

Readiness checks are added by calling AddReadinessCheck() function of tpl instance.

Please note, that every value in check parameters is interpolated.

Currently available readiness checks include:


As the name suggests this readiness check is used to ensure readiness of a http service[s].

Availalable parameters include:

  • url :: string - A HTTP URL to try fetching.
  • codes :: [int] - A list of successful HTTP response codes. At lest one must match in order for a check to be considered successful.
  • headers :: [object] - A list of header objects to match. Values within the same objects are matched in a conjuctive way (AND). Values from different objects are matched in a disjunctive way (OR).
  • body :: string - A regexp to match response body against.
  • retry_limit :: int - How many times to retry a check before giving up.
  • retry_interval :: string - How long to wait between retrying. String must follow Golang fmt.Duration format.


A simple low-level network readiness check. protocol and address parametes must be formatted according to Golang net.Dial function.

Availalable parameters include:

  • protocol :: string - Network protocol
  • address :: string - Address string
  • retry_limit :: int - How many times to retry a check before giving up.
  • retry_interval :: string - How long to wait between retrying. String must follow Golang fmt.Duration format.

Helper JS functions

In addition to image and container specific APIs there are also some additional helper modules which can be used directly anywhere in the template script.

fmt(format :: string, args :: any...)

A useful shorthand for printing formatted messages. It's nothing more than an exported Golang function fmt.Printf.


type module contains functions related to managing types.

All Ensure* functions take a value and panic if the value is not of correspdonging type. It passes otherwise (including value not being defined).

type.EnsureString(arg :: any)
type.EnsureNumber(arg :: any)
type.EnsureListOfStrings(arg :: any)
type.EnsureListOfNumbers(arg :: any)
type.FromBase64(name :: string, value :: string)

Decodes a value from base64 string to a byte array. name argument is only used for logging in case of errors.

type.IsArray(arg :: any)

Returns true if given argument is of array type.

type.IsDefined(arg :: any)

Returns true if given argument is neither null nor undefined.


Sometimes a static file, either embedded into an image or mounted into a container in runtime is not enough, we need to be able to include some dynamic parts, parts which can take different values from environment to environment. For example you may need to specify a database address in a config for your service. But the hostname will always be different, you cannot just hardcode it.

This is where interpolation kicks in. Interpolation is just a fancy name for variable substitution. Basically you just reserve certain placeholders in your configs and they will be filled with needed values in due time.

There are two main types of interpolation in xenvman:

  1. Workspace files
  2. Mounted files, readiness checks and environ interpolation

The main difference between them is the available data.

For workspace files the only data you can substitute is the one you supply yourself. The reason for this is that workspace files are baked into an image and thus cannot be modified in any way during container lifetime.

All the rest, on the other hand, do have access to some runtime info like containers, ports etc.

All the interpolation is done using Golang template language.

Workspace files interpolation

Workspace files interpolation is very simple, you just call InterpolateWorkspaceFile() function on a file you want to interpolate. You must copy the file using CopyDataToWorkspace() or AddFileToWorkspace() first.

You can supply arbitrary object and its fields in your interpolation placeholders.

For example, let's say we have a Dockerfile in our data dir. It will be included into an image every time we build it. And we allow clients to supply their own executable binary. Thus we don't know what the binary will be so we cannot hardcode the executable name and so we'll use interpolation for it.

Let's examine template code first:

function execute(tpl, params) {
    var img = tpl.BuildImage("service-%s", params.service);
    img.InterpolateWorkspaceFile("Dockerfile", {"service": params.service});

And the Dockerfile itself:

FROM ubuntu

COPY {{.service}} /
CMD ["/{{.service}}", "run"]

Here {{.service}} will be substituted with whaterver was provided in

    img.InterpolateWorkspaceFile("Dockerfile", {"service": params.service});

in our template.

Mounted files, readiness checks & environ interpolation

For this type of interpolation, in addition to providing your own placeholder data, there's also some internal environment-specific data available for you.

Let's take a look at what's available:

.Self -> Container

Return a current container instance.

.Extra -> Any

Returns a user-provided data, if any.

.ExternalAddress -> string

Returns an external address.

.ContainersWithLabels(label : string, value : string) -> [Container]

Find all containers with a given label name and value. Empty value matches any label.

.ContainerWithLabel(label : string, value : string) -> Container

Find a container with a given label name and value. Empty value matches any label.

.AllContainers() -> [Container]

Return a list of all containers in the environment.

Container instance methods

.IP -> string

Returns internal container IP address.

.Hostname -> string

Returns container hostname.

.Name -> string

Returns container name.

.GetLabel(label : string) -> string

Returns label value. Empty string is returned if there's no such label on the container.

.ExposedPort(iport : int) -> int

Returns an external (exposed) port for the given internal one. It's an error if there's no such port exposed on the container.


xenvman exposes all its functionality using HTTP API.

GET /api/v1/env

List active environments.

Response body


POST /api/v1/env

Create a new environment.



Response body


GET /api/v1/env/{id}

Get environment info.

Response body


PATCH /api/v1/env/{id}

Update existing environment.



Response body


DELETE /api/v1/env/{id}

Delete an environment.

Query parameters

  • id - Environment id

POST /api/v1/env/{id}/keepalive

Keep alive an environment.

A client can periodicall call this endpoint in order to keep the environment running. Otherwise an environment will be terminated after the configured keepalive interval.

GET /api/v1/tpl

Get templates info.

Response body

{name: string -> TplInfo}



   // Environment name
   name: string,
   // Environment description
   description: string,
   // Templates to use
   templates: [InputTpl]

   // Additional env options
   options: InputEnvOptions


  // Environment keep alive setting
  keep_alive: string,
  // Whether to disable dynamic discovery DNS agent and revert back to static
  // hostnames
  disable_discovery: bool


    // Environment id
    id: string,
    // Environment name
    name: string,
    // Environment description
    description: string,
    // Workspace directory
    ws_dir: string,
    // Mount directory
    mount_dir: string,
    // Container engine network id for the environment
    net_id: string,
    // Creation time
    created: string,
    // Environment keep alive setting
    keep_alive: string,
    // External address (hostname or IP) of the xenvman server
    external_address: string,
    // Templates data
    templates: {name: string -> [TplData]}


   // A list of fully-qualified container names to stop
   stop_containers: [string],
   // A list of fully-qualified container names to restart
   start_containers: [string],
   // New templates to execute
   templates: [InputTpl]


  // Template name (a path relative to xenvman base template dir)
  tpl: string,
  // Template parameters as arbitrary JSON object
  parameters: object 


   // Template containers
   containers: {name: string -> [ContainerData]}


   // Unique container id
   id: string,
   // Internal container hostname
   hostname: string,
   // Mapping between internal container port and corresponding external one
   ports: {port: string -> int}


   // Template description
   description: string,
   // Template parameters
   parameters: {name: string -> TplInfoParam},
   // List of files in template data directory
   data_dir: [string]


   // Parameter description
   description: string,
   // Parameter type
   type: string,
   // Whether a parameter is mandatory
   mandatory: bool,
   // Default value
   default: any,

Dynamic discovery

In the version v2.0.0 a new dynamic discovery agent has been introduced. It is basically a simple DNS proxy configurable over HTTP which all the containers running inside an environment are configured to use. This allows us to dynamicall re-configure environment on-the-fly, add/update/stop containers and make sure newly added containers can be discovered by the old ones.

The discovery agent is injected as just any another template and a tiny image from docker hub is fetched with size of about 8 mb. This template creates a single container with a running agent. The hostname of the container is discovery.0.discovery.xenv and it exposes port 8080 over which it is configured later by xenvman server.

You can disable this feature and opt in for static DNS config by setting disable_discovery=true env option. If you do this though, you will not be able to dynamically change the environment composition (add/stop containers) after it has started.

By default discovery agent is enabled.

The following picture illustrates these two different approaches:

Static vs Dynamic DNS configuration

Dynamic environment reconfiguration

Starting from version v2.0.0 it is possible to change environment composition while it is running. One can stop existing containers (perhaps to emulate network split) or inject new templates and introduce new containers (peers arrival). A new API endpoint have been added for this purpose: PATCH /api/v1/env/{id}.

Please note: the environment reconfiguration is only available if dynamic agent has not been disabled.

Web UI

Starting from version v2.0.0 xenman has a simple embedded web application. It can be used to:

  • Inspect currently running environments
  • Terminate an environment
  • Browse through all available templates
  • Inspect invidual templates and its parameters

Once xenvman is running simply point your browser at http://<HOST>:<PORT>/, where <HOST> is the hostname/ip where xenvman is running and <PORT> is the post which xenvman is listening on.

List of active environments: List of environments

Environment info: Environment info

Templates browser: Templates browser


Because xenvman uses plain HTTP API, any language/tool capable of talking HTTP can be used as a client. But it's arguably easier to have native and idiomatic libraries for a language of choice, especially to embed managing environments directly into integration tests themselves.

Currently xenvman supports the following language clients:


Go documentation for client package is available here.

An example of how to use the client API is available in xenvman-tutorial.


Python client is available here.