SLA - Application Controller - stop and start appliances based on performance and resource metrics

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SLA - Application Controller - stop and start appliances based on performance and resource metrics

Latest version:

SLA 1.1.5-1
SLACTL 2.0.2-1

SLA: Controller


At a Glance
Catalog	Dynamic
Category	Application Controller
User volumes	yes
Min. memory	224 MB
OS	Linux
Constraints	no
Questions/Comments	Ask Forum

Functional Overview

SLA is an application controller which dynamically scales an application by starting and stopping other appliances within the application in accordance with a user-defined policy. Policy enforcement relies on periodic assessment of counter values accessed through the mtr terminal. The mtr terminal is typically connected to the aux terminal of the MON appliance. SLA tracks the values of a single counter over a group of appliances.

The policy is configurable through a simple web interface (GUI) exposed by SLA. The GUI is accessed using the application IP and the configured SLA port. A policy comprises:

counter entity (that is, CPU Summary)
counter name (that is, CPU Total)
start value (that is, 30)
stop value (that is, 10)
trailing average period (that is, 15 minutes)

SLA periodically calculates a trailing average for the counter by averaging the counter values of the running appliances in the appliance group over the trailing average period. When the trailing average passes the start value, SLA starts an appliance in the appliance group. When the trailing average passes the stop value, SLA stops an appliance in the appliance group.

SLA is typically used to start and stop individual web servers within the scalable web server appliances WEBx4/WEBx8 in response to HTTP request load.

Important

SLA works only with MON appliances version 1.1.3 and above. To verify the version of any MON appliance in your application, right-click on the appliance and select view class.

The SLA appliance is an assembly comprised of an instance of the PS8 port switch and an instance of the SLACTL appliance. The SLACTL appliance is not designed to be used independent of the containing SLA assembly. Use the SLA appliance when designing an application rather than directly using the SLACTL appliance.

Boundary

Resources

Resource	Minimum	Maximum	Default
CPU	0.1	0.1	0.1
Memory	224 MB	224 MB	224 MB
Bandwidth	1 Mbps	1 Mbps	1 Mbps

Terminals

Name	Direction	Protocol	Description
in	in	Any	Exposes a web interface (GUI) for configuring the policy. All other network traffic not directed to the GUI is passed-through aux without modification.
net	out	Any	Output for accessing the grid to facilitate appliance start/stop.
mtr	out	Any	Output for accessing performance and resource data using the MON Data Collection Interface.
log	out	CIFS	Output to a network file system for storing operational logs. If this terminal is unconnected, logs are stored on the config volume.
aux	out	Any	Auxiliary output. Incoming traffic that is not directed to the GUI is sent through this terminal without modification. This terminal can be left unconnected.
mon	out	CCE	Used for performance and resource usage statistics. This terminal can be left unconnected.

User Volumes

Volume	Description
config	Read/write volume for configuration data.

This volume is used to store:

a private key file which provides authentication as a normal user on the grid controller
the policy
temporary files
a log of SLA operations (provided the log terminal is unconnected)

This volume should be 10MB in size. See Preparing for Use for information about setting up a private key on the config volume.

Properties

name	type	description
appliance_group	string	The group of appliances which SLA dynamically starts and stops. This is an appliance name excluding any trailing numbers. For example, a value of main.srv.srv indicates that SLA will start/stop appliances whose names begin with main.srv.srv (that is, main.srv.srv1, main.srv.srv2, and so on.) This property is mandatory.
grid_ctl_ip	IP	IP address of the grid controller on which the application is running. This property is mandatory.
port_no	integer	Port for accessing the web interface. The GUI is accessed through the application IP and this port. Default: 8080.
username	string	User name for web-based authentication. If empty, no authentication is performed. Default: empty
password	string	Password for web-based authentication. This property is not used if username is empty. Default: empty
logs_base_dir	string	Directory where logs are stored. This property has no affect if the log terminal is not connected. Default: /

Performance

Additional resources do not affect performance.

Error Messages

The following messages may appear in either the appliance log file or the system log of the grid controller when the appliance fails to start:

httpd did not start
sla setup failed
/var/www/html/.rc.local script is not executable
/var/www/html/.rc.local script failed, ret=ret

Interior

The SLA appliance is an assembly comprised of an instance of the PS8 port switch ps and an instance of the SLACTL appliance ctl as shown in the diagram below.

Important: The SLACTL appliance is not designed to be used independent of the containing SLA assembly. Use the SLA appliance when designing an application rather than directly using the SLACTL appliance.

Operational Constraints and Behavior

SLA tracks the values of only a single counter (that is, Total CPU Usage) for all the running appliances in the appliance_group (that is, web servers within a scalable web server appliance such as WEBx4 or WEBx8).
When the trailing average of the counter falls outside of the configured range, SLA starts or stops an appliance in the appliance_group.
SLA never stops all appliances with the appliance_group.
If all appliances within the appliance_group are running and the trailing average passes beyond the start value, SLA logs a message on the CA 3Tera AppLogic Dashboard.
Counter data is collected from the mtr terminal every 5 seconds.
Counter data is retained to an historical depth of 24 hours.
Policy enforcement occurs once per minute.
Once an appliance is started or stopped, policy enforcement does not resume until 6 minutes later.

Web Interface (GUI)

SLA exposes a web interface which is used to define the policy. This GUI is accessed using the application IP on the configured port port_no.

The Commit button commits the policy defined in the GUI for enforcement.

SLA GUI when a policy is being enforced

Above is an example of the GUI when a policy is being enforced. The graph shows the last 24 hours of policy enforcement and includes:

a graph of the counter values averaged over the running appliances
a graph of the trailing average
a graph of the number of running appliances in appliance_group
a horizontal line marking the start value
a horizontal line marking the stop value
a dashed vertical line marking the trailing average period

The buttons at the top of the GUI are used to:

Stop enforcement of the policy. While enforcement is stopped, SLA will not start or stop appliances in accordance with the policy.
Start enforcement of the policy. SLA resumes enforcement and will start and stop appliances in accordance with the policy.
Edit the policy.
Contract the graph width.
Expand the graph width.
Manually stop an appliance in appliance_group.
Manually start an appliance in appliance_group.

Preparing to Use SLA in an Application

The following steps must be taken before SLA can be used to dynamically start and stop appliances within an application.SLA must be able to authenticate on the grid controller as a normal user.

To prepare to use SLA in an Application

Create a public/private key pair in openssh format without a passphrase.
Create a user on the grid whose public key corresponds to the generated public key.
Put the generated private key file, with the name grid.private.key, on the root of the config volume of the appliance (such as /mnt/config/ folder) by performing one of the following procedures:
- Open Manage volumes dialog from the infrastructure editor -> Select the volume associated with SLA appliance -> Click Manage to open Volume Manage browser Window -> Upload the grid.private.key file to /mnt/config directory

Start the application in debug mode and copy the grid.private.key in /mnt/config/ folder on the SLA appliance.

Typical Usage

LampX4

The diagram below shows how SLA can be incorporated in the LampX4 reference application. The INSSLR gateway properties are set to forward tcp traffic on port 8080 to its aux terminal. Pointing a browser at port 8080 of the LampX4 application IP or resolvable domain name brings up the web interface for SLA.

Notes:

The SLA appliance should not be connected directly between an IN gateway and the rest of the application, but rather to the aux terminal of an INSSLR gateway.
A new gateway, INSSLR is available. The gateway provides the real IP address in the X-Forwarded-For http header field and is OK to use even though the SSL support is not used.

SLA appliance

Notes

It is good practice to set the username and password properties of SLA to prevent unauthorized users from accessing the SLA GUI.
If SLA fails to start or stop an appliance in appliance_group, a message is logged on the CA 3Tera AppLogic Dashboard. SLA will not try to start or stop the failed appliance again until SLA has been re-started.
On start SLA accesses the grid controller through its net terminal. SLA must start after any appliance connected to its net terminal.
SLA fails to start if any of these conditions is true:
- The property grid_ctl_ip is incorrect
- The grid.private.key file does not exist
- The grid.private.key file does not authenticate on the grid controller

The appliance_group property does not resolve to two or more appliances within the application.

Open source and 3rd party software used inside of the appliance

SLA is a compound appliance comprised of PS8 and SLACTL. The base class of SLACTL is WEB5. There are no open source 3rd party software packages installed on SLACTL in addition to those found on its base class WEB5.