VSS
Distributed Systems @ HSR
Distributed Systems @ HSR
Set of flashcards Details
| Flashcards | 61 |
|---|---|
| Language | Deutsch |
| Category | Computer Science |
| Level | University |
| Created / Updated | 06.08.2020 / 10.08.2020 |
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What are some properties of UTXO-based blockchains?
- every referenced input must be valid and not yet spent
- total value of inputs must equal or exceed total value of outputs
- transaction must have signature matching owner of input(s)
What are some properties of account-based blockchains?
- global state stores list of account with balances and code
- transaction is valid if sending account has enough balance
- if receiving account has code, code runs, state may be changed
What are atomic swaps?
an atomic cross-chain swap is a distributed coordination task where multiple parties exchange assets across multiple blockchains, e.g. BTC for ETH
What does DNSSEC ensure, what does it not ensure?
- ensures that a DNS entry wasn't modified
- provides integrity, but not availability or confidentiality
How does DNS over HTTP work?
- requests are made via HTTP
- responses returned in UDP HTTPS response
- protected from man-in-the-middle attacks
How does DNS over TLS work?
Uses the TLS protocol for DNS queries.
[Prüfungsvorbereitung Beispiel Frage]
Diese daten müssen möglichst effizient übertragen werden versuchen sie mal so ein Protokoll zu entwickeln
TODO
What are the advantages of DoH?
- confidentiality of lookups during transit
- HTTP/2 port 443
- Cannot distinguish between traffic/DNS
- responses served like simple web pages
- Performance: TCP+TLS handshake → 2/3 RTT
- DNS queries from JavaScript
List some facts about DoT.
- confidentiality of lookups during transit
- DNS over TLS port 853
- Widely supported
- Performance: TCP+TLS handshake → 2/3 RTT
- Easy upgrade clients can test if the configured resolver supports DoT on port 853, fall back to DoU53 otherwise)
List some facts about DNS load balancing.
- round robin
- split horizon DNS possible (different answer depending on source of request)
- anycast possible
On which layers can software loadbalancers operate?
Give a definition of load balancing.
Load balancing is the distribution of workloads (requests) across multiple computing resources (machines).
Should distributed systems hide their distributed nature?
How many transactions is the Ethereum blockchain capable of per day?
~826'000
How big is a block in Ethereum?
~25KB
Which parts does the CAP theorem consist of?
Consistency
Availability
Partition-tolerance
What does consistency (CAP Theorem) mean?
every node has the same consistent state
What does availability (CAP Theorem) mean?
Every non-failing node always returns a response
What does partition-tolerance (CAP Theorem) mean?
The system continues to be consistent even when network paritions
What is vertical scaling?
More hardware in the same machine
What does horizontal scaling mean?
multiple machines
What are the advantages of vertical scaling?
- lower cost at small scale
- no adaption of software required
- less administrative effort
- less power consumption
What are disadvantages of vertical scaling?
- risk of HW failure causing outage / more difficult to add fault tolerance
- HW limits for scaling / limited by moores law
What are the advantages of horizontal scaling?
- lower cost at massive scale
- easier to add fault tolerance
- higher availability
What are the disadvantages of horizontal scaling?
- adaption of software required
- more complex systems and more components are involved
- more power consumtion
Name 3 reasons for distributed system
- scaling
- location
- fault tolerance
What are the two categories of distributed systems?
- controlled distributed systems
- fully decentralized systems
What are some aspects of controlled distributed systems?
- 1 responsible organization
- low churn
- secure environment
- high availibility
- can be homogeneous / heterogeneous
- consistency
What are some aspects of fully decentralized systems?
- N responsible organizations
- High churn
- hostile environment
- unpredictable availability
- is heterogeneous
- weak consistency
List the 7 types of transparency in the context of distributed systems
- location transparency
- access transparency
- migration, relocation transparency
- replication transparency
- concurrent transparency
- failure transparency
- security transparency
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