Mesos provides mechanisms to reserve resources in specific slaves. The concept was first introduced with static reservation in 0.14.0 which enabled operators to specify the reserved resources on slave startup. This was extended with dynamic reservation in 0.23.0 which enabled operators and authorized frameworks to dynamically reserve resources in the cluster.
In both types of reservations, resources are reserved for a role.
An operator can configure a slave with resources reserved for a role. The reserved resources are specified via the --resources flag. For example, suppose we have 12 CPUs and 6144 MB of RAM available on a slave and that we want to reserve 8 CPUs and 4096 MB of RAM for the ads role. We start the slave like so:
$ mesos-slave \
--master=<ip>:<port> \
--resources="cpus:4;mem:2048;cpus(ads):8;mem(ads):4096"
We now have 8 CPUs and 4096 MB of RAM reserved for ads on this slave.
CAVEAT: In order to modify a static reservation, the operator must drain and restart the slave with the new configuration specifed in the --resources flag.
NOTE: This feature is supported for backwards compatibility. The recommended approach is to specify the total resources available on the slave as unreserved via the --resources flag and manage reservations dynamically via the master HTTP endpoints.
As mentioned in Static Reservation, specifying the reserved resources via the --resources flag makes the reservation static. This is, statically reserved resources cannot be reserved for another role nor be unreserved. Dynamic Reservation enables operators and authorized frameworks to reserve and unreserve resources post slave-startup.
We require a principal from the operator or framework in order to authenticate/authorize the operations. Permissions are specified via the existing ACL mechanism. To use authorization with reserve/unreserve operations, the Mesos master must be configured with the desired ACLs. For more information, see the authorization documentation.
Offer::Operation::Reserve and Offer::Operation::Unreserve messages are available for frameworks to send back via the acceptOffers API as a response to a resource offer./reserve and /unreserve HTTP endpoints allow operators to manage dynamic reservations through the master. NOTE: As of 0.27.0, these endpoints cannot be used when HTTP authentication is disabled due to the current implementation. This will change in version 0.28.0.In the following sections, we will walk through examples of each of the interfaces described above.
Note that if two dynamic reservations are made for resources at a single slave, the reservations will be combined by adding together the resources reserved by each request. Similarly, “partial” unreserve operations are allowed: an unreserve operation can release only some of the resources at a slave that have been reserved for a given role. In this case, the unreserved resources will be subtracted from the previous reservation, and any remaining resources will still be reserved.
Offer::Operation::ReserveA framework can reserve resources through the resource offer cycle. Suppose we receive a resource offer with 12 CPUs and 6144 MB of RAM unreserved.
{
"id": <offer_id>,
"framework_id": <framework_id>,
"slave_id": <slave_id>,
"hostname": <hostname>,
"resources": [
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 12 },
"role": "*",
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 6144 },
"role": "*",
}
]
}
We can reserve 8 CPUs and 4096 MB of RAM by sending the following Offer::Operation message. Offer::Operation::Reserve has a resources field which we specify with the resources to be reserved. We need to expicitly set the role and principal fields with the framework's role and principal.
{
"type": Offer::Operation::RESERVE,
"reserve": {
"resources": [
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
}
]
}
}
If the reservation is successful, a subsequent resource offer will contain the following reserved resources:
{
"id": <offer_id>,
"framework_id": <framework_id>,
"slave_id": <slave_id>,
"hostname": <hostname>,
"resources": [
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
]
}
Offer::Operation::UnreserveA framework can unreserve resources through the resource offer cycle. In Offer::Operation::Reserve, we reserved 8 CPUs and 4096 MB of RAM on a particular slave for our role. The master will continue to only offer these resources to our role. Suppose we would like to unreserve these resources. First, we receive a resource offer (copy/pasted from above):
{
"id": <offer_id>,
"framework_id": <framework_id>,
"slave_id": <slave_id>,
"hostname": <hostname>,
"resources": [
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
]
}
We can unreserve the 8 CPUs and 4096 MB of RAM by sending the following Offer::Operation message. Offer::Operation::Unreserve has a resources field which we can use to specify the resources to be unreserved.
{
"type": Offer::Operation::UNRESERVE,
"unreserve": {
"resources": [
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": <framework_role>,
"reservation": {
"principal": <framework_principal>
}
}
]
}
}
The unreserved resources may now be offered to other frameworks.
As described above, dynamic reservations can be made by a framework scheduler, typically in response to a resource offer. However, dynamic reservations can also be created and deleted by sending HTTP requests to the /reserve and /unreserve endpoints, respectively. This capability is intended for use by operators and administrative tools.
/reserve (since 0.25.0)Suppose we want to reserve 8 CPUs and 4096 MB of RAM for the ads role on a slave with id=<slave_id> (note that it is up to the user to find the ID of the slave that hosts the desired resources; the request will fail if sufficient unreserved resources cannot be found on the slave). We send an HTTP POST request to the /reserve HTTP endpoint like so:
$ curl -i \
-u <operator_principal>:<password> \
-d slaveId=<slave_id> \
-d resources='[
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": "ads",
"reservation": {
"principal": <operator_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": "ads",
"reservation": {
"principal": <operator_principal>
}
}
]' \
-X POST http://<ip>:<port>/master/reserve
The user receives one of the following HTTP responses:
200 OK: Success (the requested resources have been reserved).400 BadRequest: Invalid arguments (e.g., missing parameters).401 Unauthorized: Unauthenticated request.403 Forbidden: Unauthorized request.409 Conflict: Insufficient resources to satisfy the reserve operation./unreserve (since 0.25.0)Suppose we want to unreserve the resources that we dynamically reserved above. We can send an HTTP POST request to the /unreserve HTTP endpoint like so:
$ curl -i \
-u <operator_principal>:<password> \
-d slaveId=<slave_id> \
-d resources='[
{
"name": "cpus",
"type": "SCALAR",
"scalar": { "value": 8 },
"role": "ads",
"reservation": {
"principal": <operator_principal>
}
},
{
"name": "mem",
"type": "SCALAR",
"scalar": { "value": 4096 },
"role": "ads",
"reservation": {
"principal": <operator_principal>
}
}
]' \
-X POST http://<ip>:<port>/master/unreserve
The user receives one of the following HTTP responses:
200 OK: Success (the requested resources have been unreserved).400 BadRequest: Invalid arguments (e.g., missing parameters).401 Unauthorized: Unauthenticated request.403 Forbidden: Unauthorized request.409 Conflict: Insufficient resources to satisfy the unreserve operation.