To deploy these machines, we need an external solution. Some solutions are:
- Manual installations requiring somebody to obtain a few machines, manually installing operating systems (e.g. a Linux distribution), and finally installing all required software packages, such as Nix, Dysnomia, Disnix and any additional container services. Manually configuring a machine is typically tedious, time consuming and error prone.
- NixOps. NixOps is capable of automatically instantiating networks of virtual machines in the cloud (such as Amazon EC2) and deploying entire NixOS system configurations to them. These NixOS configurations can be used to automatically deploy Dysnomia, Disnix and any container service that we need. A drawback is that NixOps is NixOS-based and not really useful if you want to deploy services to machines running different kinds of operating systems.
- disnixos-deploy-network. In a Disnix-context, services are basically undefined units of deployment, and we can also automatically deploy entire NixOS configurations to target machines as services. A major drawback of this approach is that we require predeployed machines running Disnix first.
Although there are several ways to manage the underlying infrastructure of services, they are basically all or nothing solutions with regards to automation -- we either have to manually deploy entire machine configurations ourselves or we are stuck to a NixOS-based solution that completely automates it.
In some scenarios (e.g. when it is desired to deploy services to non-Linux operating systems), the initial deployment phase becomes quite tedious. For example, it took me quite a bit of effort to set up the heterogeneous network deployment demo I have given at NixCon2015.
In this blog post, I will describe an approach that serves as an in-between solution -- since services in a Disnix-context can be (almost) any kind of deployment unit, we can also use Disnix to deploy container configurations as services. These container services can also be deployed to non-NixOS systems, which means that we can alleviate the effort in setting up the initial target system configurations where Disnix can deploy services to.
Deploying containers as services with Disnix
As with services, containers in a Disnix-context could take any form. For example, in addition to MySQL databases (that we can deploy as services with Disnix), we can also deploy the corresponding container: the MySQL DBMS server, as a Disnix service:
{ stdenv, mysql, dysnomia
, name ? "mysql-database"
, mysqlUsername ? "root", mysqlPassword ? "secret"
, user ? "mysql-database", group ? "mysql-database"
}:
stdenv.mkDerivation {
inherit name;
buildCommand = ''
mkdir -p $out/bin
# Create wrapper script
cat > $out/bin/wrapper <<EOF
#! ${stdenv.shell} -e
case "\$1" in
activate)
# Create group, user and the initial database if it does not exists
# ...
# Run the MySQL server
${mysql}/bin/mysqld_safe --user=${user} --datadir=${dataDir} --basedir=${mysql} --pid-file=${pidDir}/mysqld.pid &
# Change root password
# ...
;;
deactivate)
${mysql}/bin/mysqladmin -u ${mysqlUsername} -p "${mysqlPassword}" -p shutdown
# Delete the user and group
# ...
;;
esac
EOF
chmod +x $out/bin/wrapper
# Add Dysnomia container configuration file for the MySQL DBMS
mkdir -p $out/etc/dysnomia/containers
cat > $out/etc/dysnomia/containers/${name} <<EOF
mysqlUsername="${mysqlUsername}"
mysqlPassword="${mysqlPassword}"
EOF
# Copy the Dysnomia module that manages MySQL databases
mkdir -p $out/etc/dysnomia/modules
cp ${dysnomia}/libexec/dysnomia/mysql-database $out/etc/dysnomia/modules
'';
}
The above code fragment is a simplified Disnix expression that can be used to deploy a MySQL server. The above expression produces a wrapper script, which carries out a set of deployment activities invoked by Disnix:
- On activation, the wrapper script starts the MySQL server by spawning the mysqld_safe daemon process in background mode. Before starting the daemon, it also intitializes some of the server's state, such as creating user accounts under which the daemon runs and setting up the system database if it does not exists (these steps are left out of the example for simplicity reasons).
- On deactivation it shuts down the MySQL server and removes some of the attached state, such as the user accounts.
Besides composing a wrapper script, we must allow Dysnomia (and Disnix) to deploy databases as Disnix services to the MySQL server that we have just deployed:
- We generate a Dysnomia container configuration file with the MySQL server settings to allow a database (that gets deployed as a service) to know what credentials it should use to connect to the database.
- We bundle a Dysnomia plugin module that implements the deployment activities for MySQL databases, such as activation and deactivation. Because Dysnomia offers this plugin as part of its software distribution, we make a copy of it, but we could also compose our own plugin from scratch.
With the earlier shown Disnix expression, we can define the MySQL server as a service in a Disnix services model:
mysql-database = {
name = "mysql-database";
pkg = customPkgs.mysql-database;
dependsOn = {};
type = "wrapper";
};
and distribute it to a target machine in the network by adding an entry to the distribution model:
mysql-database = [ infrastructure.test2 ];
Configuring Disnix and Dysnomia
Once we have deployed containers as Disnix services, Disnix (and Dysnomia) must know about their availability so that we can deploy services to these recently deployed containers.
Each time Disnix has successfully deployed a configuration, it generates Nix profiles on the target machines in which the contents of all services can be accessed from a single location. This means that we can simply extend Dysnomia's module and container search paths:
export DYSNOMIA_MODULES_PATH=$DYSNOMIA_MODULES_PATH:/nix/var/nix/profiles/disnix/containers/etc/dysnomia/modules export DYSNOMIA_CONTAINERS_PATH=$DYSNOMIA_CONTAINERS_PATH:/nix/var/nix/profiles/disnix/containers/etc/dysnomia/containers
with the paths to the Disnix profiles that have containers deployed.
A simple example scenario
I have modified the Java variant of the ridiculous Disnix StaffTracker example to support a deployment scenario with containers as Disnix services.
First, we need to start with a collection of machines having a very basic configuration without any additional containers. The StaffTracker package contains a bare network configuration that we can deploy with NixOps, as follows:
$ nixops create ./network-bare.nix ./network-virtualbox.nix -d vbox $ nixops deploy -d vbox
By configuring the following environment variables, we can connect Disnix to the machines in the network that we have just deployed with NixOps:
$ export NIXOPS_DEPLOYMENT=vbox $ export DISNIX_CLIENT_INTERFACE=disnix-nixops-client
We can write a very simple bootstrap infrastructure model (infrastructure-bootstrap.nix), to dynamically capture the configuration of the target machines:
{
test1.properties.hostname = "test1";
test2.properties.hostname = "test2";
}
Running the following command:
$ disnix-capture-infra infrastructure-bootstrap.nix > infrastructure-bare.nix
yields an infrastructure model (infrastructure-containers.nix) that may have the following structure:
{
"test1" = {
properties = {
"hostname" = "test1";
"system" = "x86_64-linux";
};
containers = {
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
"test2" = {
properties = {
"hostname" = "test2";
"system" = "x86_64-linux";
};
containers = {
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
}
As may be observed in the captured infrastructure model shown above, we have a very minimal configuration only hosting the process and wrapper containers, that integrate with host system's service manager, such as systemd.
We can deploy a Disnix configuration having Apache Tomcat and the MySQL DBMS as services, by running:
$ disnix-env -s services-containers.nix \ -i infrastructure-bare.nix \ -d distribution-containers.nix \ --profile containers
Note that we have provided an extra parameter to Disnix: --profile to isolate the containers from the default deployment environment. If the above command succeeds, we have a deployment architecture that looks as follows:
Both machines have Apache Tomcat deployed as a service and machine test2 also runs a MySQL server.
When capturing the target machines' configurations again:
$ disnix-capture-infra infrastructure-bare.nix > infrastructure-containers.nix
we will receive an infrastructure model (infrastructure-containers.nix) that may have the following structure:
{
"test1" = {
properties = {
"hostname" = "test1";
"system" = "x86_64-linux";
};
containers = {
tomcat-webapplication = {
"tomcatPort" = "8080";
};
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
"test2" = {
properties = {
"hostname" = "test2";
"system" = "x86_64-linux";
};
containers = {
mysql-database = {
"mysqlUsername" = "root";
"mysqlPassword" = "secret";
"mysqlPort" = "3306";
};
tomcat-webapplication = {
"tomcatPort" = "8080";
};
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
}
As may be observed in the above infrastructure model, both machines provide a tomcat-webapplication container exposing the TCP port number that the Apache Tomcat server has been bound to. Machine test2 exposes the mysql-database container with its connectivity settings.
We can now deploy the StaffTracker system (that consists of multiple MySQL databases and Apache Tomcat web applications) by running:
$ disnix-env -s services.nix \ -i infrastructure-containers.nix \ -d distribution.nix \ --profile services
Note that I use a different --profile parameter, to tell Disnix that the StaffTracker components belong to a different environment than the containers. If I would use --profile containers again, Disnix will undeploy the previously shown containers environment with the MySQL DBMS and Apache Tomcat and deploy the databases and web applications, which will lead to a failure.
If the above command succeeds, we have the following deployment architecture:
The result is that we have all the service components of the StaffTracker example deployed to containers that are also deployed by Disnix.
An advanced example scenario: multi-containers
We could go even one step beyond the example I have shown in the previous section. In the first example, we deploy no more than one instance of each container to a machine in the network -- this is quite common, as it rarely happens that you want to run two MySQL or Apache Tomcat servers on a single machine. Most Linux distributions (including NixOS) do not support deploying multiple instances of system services out of the box.
However, with a few relatively simple modifications to the Disnix expressions of the MySQL DBMS and Apache Tomcat services, it becomes possible to allow multiple instances to co-exist on the same machine. What we basically have to do is identifying the conflicting runtime resources, making them configurable and changing their values in such a way that they no longer conflict.
{ stdenv, mysql, dysnomia
, name ? "mysql-database"
, mysqlUsername ? "root", mysqlPassword ? "secret"
, user ? "mysql-database", group ? "mysql-database"
, dataDir ? "/var/db/mysql", pidDir ? "/run/mysqld"
, port ? 3306
}:
stdenv.mkDerivation {
inherit name;
buildCommand = ''
mkdir -p $out/bin
# Create wrapper script
cat > $out/bin/wrapper <<EOF
#! ${stdenv.shell} -e
case "\$1" in
activate)
# Create group, user and the initial database if it does not exists
# ...
# Run the MySQL server
${mysql}/bin/mysqld_safe --port=${toString port} --user=${user} --datadir=${dataDir} --basedir=${mysql} --pid-file=${pidDir}/mysqld.pid --socket=${pidDir}/mysqld.sock &
# Change root password
# ...
;;
deactivate)
${mysql}/bin/mysqladmin --socket=${pidDir}/mysqld.sock -u ${mysqlUsername} -p "${mysqlPassword}" -p shutdown
# Delete the user and group
# ...
;;
esac
EOF
chmod +x $out/bin/wrapper
# Add Dysnomia container configuration file for the MySQL DBMS
mkdir -p $out/etc/dysnomia/containers
cat > $out/etc/dysnomia/containers/${name} <<EOF
mysqlUsername="${mysqlUsername}"
mysqlPassword="${mysqlPassword}"
mysqlPort=${toString port}
mysqlSocket=${pidDir}/mysqld.sock
EOF
# Copy the Dysnomia module that manages MySQL databases
mkdir -p $out/etc/dysnomia/modules
cp ${dysnomia}/libexec/dysnomia/mysql-database $out/etc/dysnomia/modules
'';
}
For example, I have revised the MySQL server Disnix expression with additional parameters that change the TCP port the service binds to, the UNIX domain socket that is used by the administration utilities and the filesystem location where the databases are stored. Moreover, these additional configuration properties are also exposed by the Dysnomia container configuration file.
These additional parameters make it possible to define multiple variants of container services in the services model:
{distribution, invDistribution, system, pkgs}:
let
customPkgs = import ../top-level/all-packages.nix {
inherit system pkgs;
};
in
rec {
mysql-production = {
name = "mysql-production";
pkg = customPkgs.mysql-production;
dependsOn = {};
type = "wrapper";
};
mysql-test = {
name = "mysql-test";
pkg = customPkgs.mysql-test;
dependsOn = {};
type = "wrapper";
};
tomcat-production = {
name = "tomcat-production";
pkg = customPkgs.tomcat-production;
dependsOn = {};
type = "wrapper";
};
tomcat-test = {
name = "tomcat-test";
pkg = customPkgs.tomcat-test;
dependsOn = {};
type = "wrapper";
};
}
I can, for example, map two MySQL DBMS instances and the two Apache Tomcat servers to the same machines in the distribution model:
{infrastructure}:
{
mysql-production = [ infrastructure.test1 ];
mysql-test = [ infrastructure.test1 ];
tomcat-production = [ infrastructure.test2 ];
tomcat-test = [ infrastructure.test2 ];
}
Deploying the above configuration:
$ disnix-env -s services-multicontainers.nix \ -i infrastructure-bare.nix \ -d distribution-multicontainers.nix \ --profile containers
yields the following deployment architecture:
As can be observed, we have two instances of the same container hosted on the same machine. When capturing the configuration:
$ disnix-capture-infra infrastructure-bare.nix > infrastructure-multicontainers.nix
we will receive a Nix expression that may look as follows:
{
"test1" = {
properties = {
"hostname" = "test1";
"system" = "x86_64-linux";
};
containers = {
mysql-production = {
"mysqlUsername" = "root";
"mysqlPassword" = "secret";
"mysqlPort" = "3306";
"mysqlSocket" = "/run/mysqld-production/mysqld.sock";
};
mysql-test = {
"mysqlUsername" = "root";
"mysqlPassword" = "secret";
"mysqlPort" = "3307";
"mysqlSocket" = "/run/mysqld-test/mysqld.sock";
};
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
"test2" = {
properties = {
"hostname" = "test2";
"system" = "x86_64-linux";
};
containers = {
tomcat-production = {
"tomcatPort" = "8080";
"catalinaBaseDir" = "/var/tomcat-production";
};
tomcat-test = {
"tomcatPort" = "8081";
"catalinaBaseDir" = "/var/tomcat-test";
};
process = {
};
wrapper = {
};
};
"system" = "x86_64-linux";
};
}
In the above expression, there are two instances of MySQL and Apache Tomcat deployed to the same machine. These containers have their resources configured in such a way that they do not conflict. For example, both MySQL instances bind to a different TCP ports (3306 and 3307) and different UNIX domain sockets (/run/mysqld-production/mysqld.sock and /run/mysqld-test/mysqld.sock).
After deploying the containers, we can also deploy the StaffTracker components (databases and web applications) to them. As described in my previous blog post, we can use an alternative (and more verbose) notation in the distribution model to directly map services to containers:
{infrastructure}:
{
GeolocationService = {
targets = [
{ target = infrastructure.test2; container = "tomcat-test"; }
];
};
RoomService = {
targets = [
{ target = infrastructure.test2; container = "tomcat-production"; }
];
};
StaffService = {
targets = [
{ target = infrastructure.test2; container = "tomcat-test"; }
];
};
StaffTracker = {
targets = [
{ target = infrastructure.test2; container = "tomcat-production"; }
];
};
ZipcodeService = {
targets = [
{ target = infrastructure.test2; container = "tomcat-test"; }
];
};
rooms = {
targets = [
{ target = infrastructure.test1; container = "mysql-production"; }
];
};
staff = {
targets = [
{ target = infrastructure.test1; container = "mysql-test"; }
];
};
zipcodes = {
targets = [
{ target = infrastructure.test1; container = "mysql-production"; }
];
};
}
As may be observed in the distribution model above, we deploy databases and web application to both instances that are hosted on the same machine.
We can deploy the services of which the StaffTracker consists, as follows:
$ disnix-env -s services.nix \ -i infrastructure-multicontainers.nix \ -d distribution-advanced.nix \ --profile services
and the result is the following deployment architecture:
As may be observed in the picture above, we now have a running StaffTracker system that uses two MySQL and two Apache Tomcat servers on one machine. Isn't it awesome? :-)
Conclusion
In this blog post, I have demonstrated an approach in which we deploy containers as services with Disnix. Containers serve as potential deployment targets for other Disnix services.
Previously, we only had NixOS-based solutions to manage the configuration of containers, which makes using Disnix on other platforms than NixOS painful, as the containers had to be deployed manually. The approach described in this blog post serves as an in-between solution.
In theory, the process in which we deploy containers as services first followed by the "actual" services, could be generalized and extended into a layered service deployment model, with a new tool automating the process and declarative specifications capturing the properties of the layers.
However, I have decided not to implement this new model any time soon for practical reasons -- in nearly all of my experiences with service deployment, I have almost never encountered the need to have more than two layers supported. The only exception I can think of is the deployment of Axis2 web services to an Axis2 container -- the Axis2 container is a Java web application that must be deployed to Apache Tomcat first, which in turn requires the presence of the Apache Tomcat server.
Availability
I have integrated the two container deployment examples into the Java variant of the StaffTracker example.
The new concepts described in this blog post are part of the development version of Disnix and will become available in the next release.
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