diff --git a/app/controllers/submissions_controller.rb b/app/controllers/submissions_controller.rb
index 4abe2632..b01cf970 100644
--- a/app/controllers/submissions_controller.rb
+++ b/app/controllers/submissions_controller.rb
@@ -137,7 +137,7 @@ class SubmissionsController < ApplicationController
     @output = +''
 
     socket.on :output do |data|
-      Rails.logger.info("#{Time.zone.now.getutc}: Container sending: #{data}")
+      Rails.logger.info("#{Time.zone.now.getutc}: Container sending: #{data.inspect}")
       @output << data if @output.size + data.size <= max_output_buffer_size
     end
 
@@ -150,10 +150,6 @@ class SubmissionsController < ApplicationController
     end
 
     socket.on :exit do |exit_code|
-      # As this is sometimes called before the timeout is handled, we must not close the
-      # socket to the user here. The socket will be closed after handling the timeout.
-      next if exit_code == Runner::Connection::TIMEOUT_EXIT_STATUS
-
       EventMachine.stop_event_loop
       if @output.empty?
         tubesock.send_data JSON.dump({cmd: :write, stream: :stdout, data: "#{t('exercises.implement.no_output', timestamp: l(Time.zone.now, format: :short))}\n"})
diff --git a/app/models/runner.rb b/app/models/runner.rb
index 0293f181..5fd0628b 100644
--- a/app/models/runner.rb
+++ b/app/models/runner.rb
@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'forwardable'
-
 class Runner < ApplicationRecord
   belongs_to :execution_environment
   belongs_to :user, polymorphic: true
@@ -13,7 +11,6 @@ class Runner < ApplicationRecord
   STRATEGY_NAME = CodeOcean::Config.new(:code_ocean).read[:runner_management][:strategy]
   UNUSED_EXPIRATION_TIME = CodeOcean::Config.new(:code_ocean).read[:runner_management][:unused_runner_expiration_time].seconds
   BASE_URL = CodeOcean::Config.new(:code_ocean).read[:runner_management][:url]
-  DELEGATED_STRATEGY_METHODS = %i[destroy_at_management attach_to_execution copy_files].freeze
 
   attr_accessor :strategy
 
@@ -35,14 +32,20 @@ class Runner < ApplicationRecord
     runner
   end
 
-  DELEGATED_STRATEGY_METHODS.each do |method|
-    define_method(method) do |*args, &block|
-      @strategy.send(method, *args, &block)
-    rescue Runner::Error::RunnerNotFound
-      request_new_id
-      save
-      @strategy.send(method, *args, &block)
-    end
+  def copy_files(files)
+    @strategy.copy_files(files)
+  rescue Runner::Error::RunnerNotFound
+    request_new_id
+    save
+    @strategy.copy_files(files)
+  end
+
+  def attach_to_execution(command, &block)
+    @strategy.attach_to_execution(command, &block)
+  end
+
+  def destroy_at_management
+    @strategy.destroy_at_management
   end
 
   private
@@ -53,17 +56,19 @@ class Runner < ApplicationRecord
 
   def request_new_id
     strategy_class = self.class.strategy_class
-    self.runner_id = strategy_class.request_from_management(execution_environment)
-    @strategy = strategy_class.new(runner_id, execution_environment)
-  rescue Runner::Error::EnvironmentNotFound
-    if strategy_class.sync_environment(execution_environment)
-      raise Runner::Error::EnvironmentNotFound.new(
-        "The execution environment with id #{execution_environment.id} was not found and was successfully synced with the runner management"
-      )
-    else
-      raise Runner::Error::EnvironmentNotFound.new(
-        "The execution environment with id #{execution_environment.id} was not found and could not be synced with the runner management"
-      )
+    begin
+      self.runner_id = strategy_class.request_from_management(execution_environment)
+      @strategy = strategy_class.new(runner_id, execution_environment)
+    rescue Runner::Error::EnvironmentNotFound
+      if strategy_class.sync_environment(execution_environment)
+        raise Runner::Error::EnvironmentNotFound.new(
+          "The execution environment with id #{execution_environment.id} was not found and was successfully synced with the runner management"
+        )
+      else
+        raise Runner::Error::EnvironmentNotFound.new(
+          "The execution environment with id #{execution_environment.id} was not found and could not be synced with the runner management"
+        )
+      end
     end
   end
 end
diff --git a/app/models/submission.rb b/app/models/submission.rb
index 4bd2653b..11857df6 100644
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -184,18 +184,10 @@ class Submission < ApplicationRecord
 
   private
 
-  def copy_files_to(runner)
-    files = {}
-    collect_files.each do |file|
-      files[file.name_with_extension] = file.content
-    end
-    runner.copy_files(files)
-  end
-
   def prepared_runner
     request_time = Time.zone.now
     runner = Runner.for(user, exercise)
-    copy_files_to runner
+    runner.copy_files(collect_files)
     waiting_duration = Time.zone.now - request_time
     yield(runner, waiting_duration)
   end
@@ -270,7 +262,7 @@ class Submission < ApplicationRecord
     update(score: score)
     if normalized_score.to_d == 1.0.to_d
       Thread.new do
-        RequestForComment.find_each(exercise_id: exercise_id, user_id: user_id, user_type: user_type) do |rfc|
+        RequestForComment.where(exercise_id: exercise_id, user_id: user_id, user_type: user_type).find_each do |rfc|
           rfc.full_score_reached = true
           rfc.save
         end
diff --git a/lib/docker_container_pool.rb b/lib/docker_container_pool.rb
index 85ea7381..a290c82c 100644
--- a/lib/docker_container_pool.rb
+++ b/lib/docker_container_pool.rb
@@ -3,6 +3,11 @@
 require 'concurrent/future'
 require 'concurrent/timer_task'
 
+# get_container, destroy_container was moved to lib/runner/strategy/docker_container_pool.rb.
+# return_container is not used anymore because runners are not shared between users anymore.
+# create_container is done by the DockerContainerPool.
+# dump_info and quantities are still in use.
+
 class DockerContainerPool
   def self.config
     # TODO: Why erb?
@@ -22,6 +27,7 @@ class DockerContainerPool
     nil
   end
 
+  # not in use because DockerClient::RECYCLE_CONTAINERS == false
   def self.return_container(container, execution_environment)
     Faraday.get("#{config[:location]}/docker_container_pool/return_container/#{container.id}")
   rescue StandardError => e
diff --git a/lib/runner/connection.rb b/lib/runner/connection.rb
index 8dd8f348..4bf725af 100644
--- a/lib/runner/connection.rb
+++ b/lib/runner/connection.rb
@@ -7,10 +7,13 @@ class Runner::Connection
   # These are events for which callbacks can be registered.
   EVENTS = %i[start output exit stdout stderr].freeze
   BACKEND_OUTPUT_SCHEMA = JSONSchemer.schema(JSON.parse(File.read('lib/runner/backend-output.schema.json')))
-  TIMEOUT_EXIT_STATUS = -100
 
-  def initialize(url)
+  attr_writer :status
+
+  def initialize(url, strategy)
     @socket = Faye::WebSocket::Client.new(url, [], ping: 5)
+    @strategy = strategy
+    @status = :established
 
     # For every event type of faye websockets, the corresponding
     # RunnerConnection method starting with `on_` is called.
@@ -37,18 +40,19 @@ class Runner::Connection
 
   private
 
-  def decode(event)
-    JSON.parse(event).deep_symbolize_keys
+  def decode(_raw_event)
+    raise NotImplementedError
   end
 
-  def encode(data)
-    data
+  def encode(_data)
+    raise NotImplementedError
   end
 
-  def on_message(event)
-    return unless BACKEND_OUTPUT_SCHEMA.valid?(JSON.parse(event.data))
+  def on_message(raw_event)
+    event = decode(raw_event)
+    return unless BACKEND_OUTPUT_SCHEMA.valid?(event)
 
-    event = decode(event.data)
+    event = event.deep_symbolize_keys
     # There is one `handle_` method for every message type defined in the WebSocket schema.
     __send__("handle_#{event[:type]}", event)
   end
@@ -60,10 +64,20 @@ class Runner::Connection
   def on_error(_event); end
 
   def on_close(_event)
-    @exit_callback.call @exit_code
+    case @status
+      when :timeout
+        raise Runner::Error::ExecutionTimeout.new('Execution exceeded its time limit')
+      when :terminated
+        @exit_callback.call @exit_code
+      else # :established
+        # If the runner is killed by the DockerContainerPool after the maximum allowed time per user and
+        # while the owning user is running an execution, the command execution stops and log output is incomplete.
+        raise Runner::Error::Unknown.new('Execution terminated with an unknown reason')
+    end
   end
 
   def handle_exit(event)
+    @status = :terminated
     @exit_code = event[:data]
   end
 
@@ -82,7 +96,6 @@ class Runner::Connection
   def handle_start(_event); end
 
   def handle_timeout(_event)
-    @exit_code = TIMEOUT_EXIT_STATUS
-    raise Runner::Error::ExecutionTimeout.new('Execution exceeded its time limit')
+    @status = :timeout
   end
 end
diff --git a/lib/runner/strategy.rb b/lib/runner/strategy.rb
index dce76adf..0007caab 100644
--- a/lib/runner/strategy.rb
+++ b/lib/runner/strategy.rb
@@ -1,8 +1,7 @@
 # frozen_string_literal: true
 
 class Runner::Strategy
-  def initialize(runner_id, environment)
-    @runner_id = runner_id
+  def initialize(_runner_id, environment)
     @execution_environment = environment
   end
 
diff --git a/lib/runner/strategy/docker.rb b/lib/runner/strategy/docker.rb
deleted file mode 100644
index fd7cfafc..00000000
--- a/lib/runner/strategy/docker.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-# frozen_string_literal: true
-
-class Runner::Strategy::Docker < Runner::Strategy; end
diff --git a/lib/runner/strategy/docker_container_pool.rb b/lib/runner/strategy/docker_container_pool.rb
new file mode 100644
index 00000000..7003f901
--- /dev/null
+++ b/lib/runner/strategy/docker_container_pool.rb
@@ -0,0 +1,138 @@
+# frozen_string_literal: true
+
+class Runner::Strategy::DockerContainerPool < Runner::Strategy
+  attr_reader :container_id, :command, :execution_environment
+
+  def self.config
+    # Since the docker configuration file contains code that must be executed, we use ERB templating.
+    @config ||= CodeOcean::Config.new(:docker).read(erb: true)
+  end
+
+  def self.request_from_management(environment)
+    container_id = JSON.parse(Faraday.get("#{config[:pool][:location]}/docker_container_pool/get_container/#{environment.id}").body)['id']
+    container_id.presence || raise(Runner::Error::NotAvailable.new("DockerContainerPool didn't return a container id"))
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to DockerContainerPool failed: #{e.inspect}")
+  rescue JSON::ParserError => e
+    raise Runner::Error::Unknown.new("DockerContainerPool returned invalid JSON: #{e.inspect}")
+  end
+
+  def initialize(runner_id, _environment)
+    super
+    @container_id = runner_id
+  end
+
+  def copy_files(files)
+    FileUtils.mkdir_p(local_workspace_path)
+    clean_workspace
+    files.each do |file|
+      if file.path.present?
+        local_directory_path = local_path(file.path)
+        FileUtils.mkdir_p(local_directory_path)
+      end
+
+      local_file_path = local_path(file.filepath)
+      if file.file_type.binary?
+        FileUtils.cp(file.native_file.path, local_file_path)
+      else
+        begin
+          File.open(local_file_path, 'w') {|f| f.write(file.content) }
+        rescue IOError => e
+          # TODO: try catch i/o exception and log failed attempts
+          # Does this fix the issue @Sebastian? What exceptions did you have in mind?
+          raise Runner::Error::Unknown.new("Could not create workspace file #{file.filepath}: #{e.inspect}")
+        end
+      end
+    end
+    FileUtils.chmod_R('+rwX', local_workspace_path)
+  end
+
+  def destroy_at_management
+    Faraday.get("#{self.class.config[:pool][:location]}/docker_container_pool/destroy_container/#{container.id}")
+  rescue Faraday::Error => e
+    raise Runner::Error::Unknown.new("Faraday request to DockerContainerPool failed: #{e.inspect}")
+  end
+
+  def attach_to_execution(command)
+    @command = command
+    starting_time = Time.zone.now
+    query_params = 'logs=0&stream=1&stderr=1&stdout=1&stdin=1'
+    websocket_url = "#{self.class.config[:ws_host]}/v1.27/containers/#{@container_id}/attach/ws?#{query_params}"
+
+    EventMachine.run do
+      socket = Connection.new(websocket_url, self)
+      EventMachine.add_timer(@execution_environment.permitted_execution_time) do
+        socket.status = :timeout
+        destroy_at_management
+      end
+      socket.send(command)
+      yield(socket)
+    end
+    Time.zone.now - starting_time # execution duration in seconds
+  end
+
+  private
+
+  def container
+    return @container if @container.present?
+
+    @container = Docker::Container.get(@container_id)
+    raise Runner::Error::RunnerNotFound unless @container.info['State']['Running']
+
+    @container
+  rescue Docker::Error::NotFoundError
+    raise Runner::Error::RunnerNotFound
+  end
+
+  def local_path(path)
+    unclean_path = local_workspace_path.join(path)
+    clean_path = File.expand_path(unclean_path)
+    unless clean_path.to_s.start_with? local_workspace_path.to_s
+      raise Runner::Error::Unknown.new("Local filepath #{clean_path.inspect} not allowed")
+    end
+
+    Pathname.new(clean_path)
+  end
+
+  def clean_workspace
+    FileUtils.rm_r(local_workspace_path.children, secure: true)
+  rescue Errno::ENOENT => e
+    raise Runner::Error::Unknown.new("The workspace directory does not exist and cannot be deleted: #{e.inspect}")
+  rescue Errno::EACCES => e
+    # TODO: Why was this rescued before @Sebastian?
+    raise Runner::Error::Unknown.new("Not allowed to clean workspace #{local_workspace_path}: #{e.inspect}")
+  end
+
+  def local_workspace_path
+    @local_workspace_path ||= Pathname.new(container.binds.first.split(':').first)
+  end
+
+  class Connection < Runner::Connection
+    def initialize(*args)
+      @stream = 'stdout'
+      super
+    end
+
+    def encode(data)
+      "#{data}\n"
+    end
+
+    def decode(raw_event)
+      case raw_event.data
+        when /@#{@strategy.container_id[0..11]}/
+          # Assume correct termination for now and return exit code 0
+          # TODO: Can we use the actual exit code here?
+          @exit_code = 0
+          @status = :terminated
+          @socket.close
+        when /#{format(@strategy.execution_environment.test_command, class_name: '.*', filename: '.*', module_name: '.*')}/
+          # TODO: Super dirty hack to redirect test output to stderr (remove attr_reader afterwards)
+          @stream = 'stderr'
+        when /#{@strategy.command}/
+        when /bash: cmd:canvasevent: command not found/
+        else
+          {'type' => @stream, 'data' => raw_event.data}
+      end
+    end
+  end
+end
diff --git a/lib/runner/strategy/poseidon.rb b/lib/runner/strategy/poseidon.rb
index 15c19da0..1938c229 100644
--- a/lib/runner/strategy/poseidon.rb
+++ b/lib/runner/strategy/poseidon.rb
@@ -62,13 +62,24 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     raise Runner::Error::Unknown.new("Error parsing response from Poseidon: #{e.message}")
   end
 
+  def initialize(runner_id, _environment)
+    super
+    @allocation_id = runner_id
+  end
+
   def copy_files(files)
+    copy = files.map do |file|
+      {
+        path: file.filepath,
+        content: Base64.strict_encode64(file.content),
+      }
+    end
     url = "#{runner_url}/files"
-    body = {copy: files.map {|filename, content| {path: filename, content: Base64.strict_encode64(content)} }}
+    body = {copy: copy}
     response = Faraday.patch(url, body.to_json, HEADERS)
     return if response.status == 204
 
-    Runner.destroy(@runner_id) if response.status == 400
+    Runner.destroy(@allocation_id) if response.status == 400
     self.class.handle_error response
   rescue Faraday::Error => e
     raise Runner::Error::Unknown.new("Faraday request to runner management failed: #{e.inspect}")
@@ -78,7 +89,7 @@ class Runner::Strategy::Poseidon < Runner::Strategy
     starting_time = Time.zone.now
     websocket_url = execute_command(command)
     EventMachine.run do
-      socket = Runner::Connection.new(websocket_url)
+      socket = Connection.new(websocket_url, self)
       yield(socket)
     end
     Time.zone.now - starting_time # execution duration
@@ -107,7 +118,7 @@ class Runner::Strategy::Poseidon < Runner::Strategy
           raise Runner::Error::Unknown.new('Poseidon did not send websocket url')
         end
       when 400
-        Runner.destroy(@runner_id)
+        Runner.destroy(@allocation_id)
     end
 
     self.class.handle_error response
@@ -116,6 +127,18 @@ class Runner::Strategy::Poseidon < Runner::Strategy
   end
 
   def runner_url
-    "#{Runner::BASE_URL}/runners/#{@runner_id}"
+    "#{Runner::BASE_URL}/runners/#{@allocation_id}"
+  end
+
+  class Connection < Runner::Connection
+    def decode(raw_event)
+      JSON.parse(raw_event.data)
+    rescue JSON::ParserError => e
+      raise Runner::Error::Unknown.new("The websocket message from Poseidon could not be decoded to JSON: #{e.inspect}")
+    end
+
+    def encode(data)
+      data
+    end
   end
 end
diff --git a/spec/lib/runner/strategy/docker_spec.rb b/spec/lib/runner/strategy/docker_container_pool_spec.rb
similarity index 62%
rename from spec/lib/runner/strategy/docker_spec.rb
rename to spec/lib/runner/strategy/docker_container_pool_spec.rb
index 4110ebf9..67c9b20f 100644
--- a/spec/lib/runner/strategy/docker_spec.rb
+++ b/spec/lib/runner/strategy/docker_container_pool_spec.rb
@@ -2,14 +2,14 @@
 
 require 'rails_helper'
 
-describe Runner::Strategy::Docker do
+describe Runner::Strategy::DockerContainerPool do
   let(:runner_id) { FactoryBot.attributes_for(:runner)[:runner_id] }
   let(:execution_environment) { FactoryBot.create :ruby }
-  let(:docker) { described_class.new(runner_id, execution_environment) }
+  let(:container_pool) { described_class.new(runner_id, execution_environment) }
 
   # TODO: add tests for these methods when implemented
   it 'defines all methods all runner management strategies must define' do
-    expect(docker.public_methods).to include(*Runner::DELEGATED_STRATEGY_METHODS)
+    expect(container_pool.public_methods).to include(:destroy_at_management, :copy_files, :attach_to_execution)
     expect(described_class.public_methods).to include(:request_from_management)
   end
 end
diff --git a/spec/lib/runner/strategy/poseidon_spec.rb b/spec/lib/runner/strategy/poseidon_spec.rb
index d3acf5f9..62bbd638 100644
--- a/spec/lib/runner/strategy/poseidon_spec.rb
+++ b/spec/lib/runner/strategy/poseidon_spec.rb
@@ -256,15 +256,15 @@ describe Runner::Strategy::Poseidon do
   end
 
   describe '#copy_files' do
-    let(:filename) { 'main.py' }
     let(:file_content) { 'print("Hello World!")' }
-    let(:action) { -> { poseidon.copy_files({filename => file_content}) } }
-    let(:encoded_file_content) { Base64.strict_encode64(file_content) }
+    let(:file) { FactoryBot.build(:file, content: file_content) }
+    let(:action) { -> { poseidon.copy_files([file]) } }
+    let(:encoded_file_content) { Base64.strict_encode64(file.content) }
     let!(:copy_files_stub) do
       WebMock
         .stub_request(:patch, "#{Runner::BASE_URL}/runners/#{runner_id}/files")
         .with(
-          body: {copy: [{path: filename, content: encoded_file_content}]},
+          body: {copy: [{path: file.filepath, content: encoded_file_content}]},
           headers: {'Content-Type' => 'application/json'}
         )
         .to_return(body: response_body, status: response_status)
diff --git a/spec/models/runner_spec.rb b/spec/models/runner_spec.rb
index e8f57966..b9395645 100644
--- a/spec/models/runner_spec.rb
+++ b/spec/models/runner_spec.rb
@@ -35,10 +35,16 @@ describe Runner do
       end
     end
 
-    {poseidon: Runner::Strategy::Poseidon, docker: Runner::Strategy::Docker}.each do |strategy, strategy_class|
+    available_strategies = {
+      poseidon: Runner::Strategy::Poseidon,
+      docker_container_pool: Runner::Strategy::DockerContainerPool,
+    }
+    available_strategies.each do |strategy, strategy_class|
       include_examples 'uses the strategy defined in the constant', strategy, strategy_class
     end
+  end
 
+  describe 'method delegation' do
     shared_examples 'delegates method sends to its strategy' do |method, *args|
       context "when sending #{method}" do
         let(:strategy) { instance_double(strategy_class) }
@@ -49,7 +55,7 @@ describe Runner do
           allow(strategy_class).to receive(:new).and_return(strategy)
         end
 
-        it "delegates the method #{method}" do
+        it 'delegates to its strategy' do
           expect(strategy).to receive(method)
           runner.send(method, *args)
         end
@@ -57,10 +63,48 @@ describe Runner do
     end
 
     include_examples 'delegates method sends to its strategy', :destroy_at_management
-    include_examples 'delegates method sends to its strategy', :copy_files, nil
     include_examples 'delegates method sends to its strategy', :attach_to_execution, nil
   end
 
+  describe '#copy_files' do
+    let(:strategy) { instance_double(strategy_class) }
+    let(:runner) { described_class.create }
+
+    before do
+      allow(strategy_class).to receive(:request_from_management).and_return(runner_id)
+      allow(strategy_class).to receive(:new).and_return(strategy)
+    end
+
+    context 'when no error is raised' do
+      it 'delegates to its strategy' do
+        expect(strategy).to receive(:copy_files).once
+        runner.copy_files(nil)
+      end
+    end
+
+    context 'when a RunnerNotFound exception is raised' do
+      before do
+        was_called = false
+        allow(strategy).to receive(:copy_files) do
+          unless was_called
+            was_called = true
+            raise Runner::Error::RunnerNotFound.new
+          end
+        end
+      end
+
+      it 'requests a new id' do
+        expect(runner).to receive(:request_new_id)
+        runner.copy_files(nil)
+      end
+
+      it 'retries to copy the files' do
+        expect(strategy).to receive(:copy_files).twice
+        runner.copy_files(nil)
+      end
+    end
+  end
+
   describe 'creation' do
     let(:user) { FactoryBot.create :external_user }
     let(:execution_environment) { FactoryBot.create :ruby }