Transcript Case Study: Distributed OS

Case Study: Distributed OS
Distributed Systems, Lecture # 17
Amoeba OS
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What if we could afford hundreds of
computers per user?
 Use
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These days this is called “blade
computing”
 Grid
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a shared pool of servers
Computing?
Location independent
 Amake
Architecture
Micro-kernel
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Process and thread (kernel/user space) management
 IPC
 Low level I/O management
 Low level Memory management
Client-Server Model
Clients are written by users
 Servers are written by system
programmers
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 Essentially
guarantees
isolating faults, and reliability
Objects
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Servers manage objects
Clients can instantiate and access objects
Objects protected by cryptographically
protected capability
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Files
 Directories
 Memory Segments
 Screen Windows
 Processors
 Disks
RPC Communication
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Primitive for location independence
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Stub acts as a proxy in the client
address space
 Resolve
name
 Marshal parameters
 Block for reply
Bullet + Soap Server
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Modular Architecture
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Naming
File Manipulation
Bullet File server
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Read-only file server
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Files can only created and deleted
Not modified!
Soap Directory Server
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Maps file names to capabilties
Other Servers
Object replication server
 Process maintenance
 Health-monitoring server
 Inter-operability servers
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Objects and Capabilities
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Objects make the system modular
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Secure
Fault-tolerant
More available
Capabilities
Naming as well as protection
 Managed in user space
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Rights management
 Can
downgrade rights of a capability
 Takes
original bits
 XOR with old rights
 Take a one-way hash
Process Management
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Process is also an object
 Accessed

by process descriptor capability
Three-levels of interfaces
 RPC
with process servers
 Library Calls
 Do-all dispatcher “Run-server”
Memory Management
Not paged or swapped
 Contiguous in memory
 Segments may be created, destroyed,
read and written
 Simple and fast in an RPC model
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 Overly
restrictive
Message passing
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Servers declare ports
 Get_port
 Identifies
a service
Clients put-ports in their messages
 At-most once semantics
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 As
opposed to atleast once
Group Communication
Closed groups
 Reliable Broadcast
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 Sequencer
model
 Lazy-ack
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Client broadcast vs Sequencer
broadcast
Layered Communication
Model
LAN
 IP
 FLIP
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 Fast
local internet protocol
 FLIP addresses are persistent and
location-independent
From the put-port to the FLIP address
 From the FLIP to the network address
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